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UNIT - I

LESSON 1: HYDROLOGICAL CYCLE

CONTENTS:

1.0 Aims and Objectives1.1 Introduction1.2 Sources of Water

1.3. Hydrologic Cycle1.3.1. Evaporation

1.3.2. Precipitation1.3.3. Infiltration1.3.4. Runoff

1.3.5 Subsurface Flow

1.4 Let Us Sum Up1.5 Lesson End Activities1.6 Points for Discussion1.7 Check your Progress Model Answers

1.8 References

1.0 AIM AND OBJECTIVES

The overall aim of this lesson is to get familiarize and understanding the sources of

water, hydrology and its components. The following are the objectives of the lesson:

1) To know the principles behind the sources of water,2) To study about hydrologic cycle in general aspect, and

3) To further understand the hydrological components like evaporation,precipitation, infiltration, runoff and subsurface flow.

1.1 INTRODUCTION

Most of the earths water sources get their water supplies from precipitation, which may

fall in various forms, such as, rain, snow, hail, dew etc. Rains no doubt, form the principal

and the major part of the resultant supplies. When rain starts falling, it is first of all

intercepted by buildings and other objects. When the rainfall rate exceeds the interception

rate, water starts reaching the ground and infiltration starts. This is the source of groundwater

storage.

1.2 SOURCES OF WATER

The primary sources of water include: rainwater, surface water (stored in lakes, streams,

and ponds), and groundwater.The distribution of water, however, is quite varied; many

locations have plenty of it while others have very little. Water exists on earth in three forms

solid (ice), liquid or gas (water vapour). Oceans, rivers, clouds, and rain, all of which contain

water, are in a frequent state of change (surface water evaporates, cloud water precipitates,

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rainfall infiltrates the ground, etc.). However, the total amount of the earth's water does not

change. Owingto glaciers, rivers and groundwater flow.

Water is essential to life. Without it, the biosphere that exists on the surface of the earth

would not be possible. The earth is called as the water planet, water's molecular

arrangement of water is very simple, two hydrogen atoms to each oxygen atom. One specialcharacteristic of water is its ability to change state very easily under earth conditions. It can

be found readily on the planet in all of its three forms, solid, liquid, and gas.

The average annual rainfall in the country is 1170 mm, which corresponds to annual

precipitation, including snowfall of 4000 Billion Cubic Metres (BCM). Out of this volume of

precipitation, only 1869 BCM appears as average annual potential flow in rivers. Due to

various constraints, only 1123 BCM is assessed as the average annual utilisable water 690

BCM from surface water and 433 BCM from groundwater.

The present total water use is 634 BCM of which 83% is for irrigation. This is projected

to grow to 813 BCM by 2010, 1093 BCM by 2025 and 1447 BCM by 2050, against utilizable

quantum of 1123 BCM. Thus the demand will outstrip availability in another 35 to 40 years.

The Central Ground Water Board has estimated the present annual groundwater draft as 231

BCM.

Self-check Exercise 1What are the major sources of water?

Note: Please proceed after answering the questionDo not write full sentences or statements; instead use words or phrases.

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1.3. HYDROLOGIC CYCLE

The movement of water on the earth's surface and through the atmosphere is known as

the hydrologic cycle. Water is taken up by the atmosphere from the earth's surface in vapour

form through evaporation. It may then be moved from place to place by the wind until it is

condensed back to its liquid phase to form clouds. Water then returns to the surface of the

earth in the form of either liquid (rain) or solid (snow, sleet, etc.) precipitation. Watertransport can also take place on or below the earth's surface by flow.

The hydrologic cycle is used to model the storage and movement of water between the

biosphere, atmosphere, lithosphere and hydrosphere. Water is stored in the following

reservoirs: atmosphere, oceans, lakes, rivers, glaciers, soils, snowfields, and groundwater. It

moves from one reservoir to another by processes like: evaporation, condensation,

precipitation, deposition, runoff, infiltration, sublimation, transpiration, and groundwater

flow.


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Water is stored in the atmosphere in all three states of matter. Water vapour in the

atmosphere is commonly referred to as humidity. If liquid and solid forms of water can

overcome atmospheric updrafts they can fall to the Earth's surface as precipitation. The

formation of ice crystals and water droplets occurs when the atmosphere is cooled to a

temperature that causes condensation or deposition. Four processes that can causeatmospheric cooling are: orographic uplift; convectional uplift; air mass convergence; and

radiative energy loss.

Precipitation can be defined as any aqueous deposit, in liquid or solid form, that

develops in a saturated atmospheric environment and generally falls from clouds. A number

of different precipitation types have been classified by meteorologists including rain, freezing

rain, snow, ice pellets, snow pellets, and hail. Fog represents the saturation of air near the

ground surface. Classification of fog types is accomplished by the identification of the

mechanism that caused the air to become saturated.

The distribution of precipitation on the Earth's surface is generally controlled by theabsence or presence of mechanisms that lift air masses to cause saturation. It is also

controlled by the amount of water vapour held in the air, which is a function of air

temperature.

In certain locations on the Earth, acid pollutants from the atmosphere are being

deposited in dry and wet forms to the Earths surface. Scientists generally call this process

acid deposition. If the deposit is wet it can also be called acid precipitation. Normally, rain is

slightly acidic. Acid precipitation, however, can have a pH as low as 2.3. Evaporation and

transpiration are the two processes that move water from the Earths surface to its

atmosphere. Evaporation is movement of free water to the atmosphere as a gas. It requires

large amounts of energy. Transpiration is the movement of water through a plant to the

atmosphere. Scientists use the term evapotranspiration to describe both processes.

In general, the following four factors control the amount of water entering the

atmosphere via these two processes: energy availability; the humidity gradient away from the

evaporating surface; the wind speed immediately above the surface; and water availability.

Agricultural scientists sometimes refer to two types of evapotranspiration: Actual

Evapotranspiration and Potential Evapotranspiration. The growth of crops is a function of

water supply. If crops experience drought, yields are reduced. Irrigation can supply crops

with supplemental water. By determining both actual evapotranspiration and potential

evapotranspiration a farmer can calculate the irrigation water needs of their crops.

The distribution of precipitation falling on the ground surface can be modified by the

presence of vegetation. Vegetation in general, changes this distribution because of the fact

that it intercepts some the falling rain. How much is intercepted is a function of the branching

structure and leaf density of the vegetation. Some of the water that is intercepted never makes

it to the ground surface. Instead, it evaporates from the vegetation surface directly back to the

atmosphere. A portion of the intercepted water can travel from the leaves to the branches and

then flow down to the ground via the plants stem. This phenomenon is called stem flow .


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Another portion of the precipitation may flow along the edge of the plant canopy to cause

canopy drip. Both of the processes described above can increase the concentration of the

water added to the soil at the base of the stem and around the edge of the plants canopy. Rain

that falls through the vegetation, without being intercepted, is called through fall.

Infiltration is the movement of water from precipitation into the soil layer. Infiltrationvaries both spatially and temporally due to a number of environmental factors. After a rain,

infiltration can create a condition where the soil is completely full of water. This condition is,

however, only short- lived as a portion of this water quickly drains (gravitational water) via

the force exerted on the water by gravity. The portion that remains is called the field capacity.

In the soil, field capacity represents a film of water coating all individual soil particles to a

thickness of 0.06 mm. The soil water from 0.0002 to 0.06 mm (known as capillary water) can

be removed from the soil through the processes of evaporation and transpiration. Both of

these processes operate at the surface. Capillary action moves water from one area in the soil

to replace losses in another area (biggest losses tend to be at the surface because of plantconsumption and evaporation). This movement of water by capillary action generally creates

a homogeneous concentration of water throughout the soil profile. Losses of water stop when

the film of water around soil particles reaches 0.0002 mm. Water held from the surface of the

soil particles to 0.0002 mm is essentially immobile and can only be completely removed with

high temperatures (greater than 100 degrees Celsius). Within the soil system, several different

forces influence the storage of water.

Runoff is the surface flow of water to areas of lower elevation. On the microscale, runoff

can be seen as a series of related events. At the global scale runoff flows from the landmasses

to the oceans. The Earths continents experience runoff because of the imbalance betweenprecipitation and evaporation.

Through flow is the horizontal subsurface movement of water on continents. Rates of

through flow vary with soil type, slope gradient, and the concentration of water in the soil.

Groundwater is the zone in the ground that is permanently saturated with water. The top of

groundwater is known as the water table. Groundwater also flows because of gravity to

surface basins of water (oceans) located at lower elevations.

The flow of water through a stream channel is commonly called stream flow or stream

discharge. On many streams humans gauge stream flow because of the hazards that can result

from too little or too much flow. Mechanical gauging devices record this information on a

graph known as a hydrograph. In the online notes there is a representation of a hydrograph

showing some of its typical features.

Oceans cover most of the Earth's surface. On average, the depth of the world's oceans is

about 3.9 kilometers. However, maximum depths can be greater than 11 kilometers. The

distribution of land and ocean surfaces on the Earth is not homogeneous. In the Southern

Hemisphere there is 4 times more ocean than land. Ratio between land and ocean is almost

equal in the Northern Hemisphere.


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The water found in the ocean is primarily a by product of the lithospheric solidification

of rock that occurred early in the Earth's history. A second source of water is volcanic

eruptions. The dissolved constituents found in the ocean come from the transport of terrestrial

salts in weathered sediments by leaching and stream runoff. Seawater is a mixture of water

and various salts. Chlorine, sodium, magnesium, calcium, potassium, and sulfur account for99 % of the salts in seawater. The presence of salt in seawater allows ice to float on top of it.

Seawater also contains small quantities of dissolved gases including: carbon dioxide, oxygen,

and nitrogen. These gases enter the ocean from the atmosphere and from a variety of organic

processes. Seawater changes its density with variations in temperature, salinity, and ocean

depth. Seawater is least dense when it is frozen at the ocean surface and contains no salts.

Highest seawater densities occur at the ocean floor.

Atmospheric circulation drives the movement of ocean currents. Within each of the

ocean, the patterns of these currents are very similar. In each basin, the ocean currents form

several closed circulation patterns known as gyres. A large gyre develops at the subtropicscentered at about 30 degrees of latitude in the Southern and Northern Hemisphere. In the

Northern Hemisphere, several smaller gyres develop with a center of rotation at 50 degrees.

Similar patterns do not develop in the middle latitudes of the Southern Hemisphere. In this

area, ocean currents are not bound by continental masses. Ocean currents differ from each

other by direction of flow, by speed of flow, and by relative temperature.

Fig 1.1: Hydrological Cycle

The planetary water supply is dominated by the oceans (Table 1.1). Approximately 97 %

of all the water on the Earth is in the oceans. The other 3 % is held as freshwater in glaciers

and icecaps, groundwater, lakes, soil, the atmosphere, and within life.


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Water is continually cycled between its various reservoirs. This cycling occurs through

the processes of evaporation, condensation, precipitation, deposition, runoff, infiltration,

sublimation, transpiration, melting, and groundwater flow. Table 1.2 describes the typical

residence times of water in the major reservoirs.


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Reservoir Volume

(Cubic km x 1,000,000)

Percent of Total

Oceans 1370 97.25

Ice Caps and Glaciers 29 2.05

Groundwater 9.5 0.68Lakes 0.125 0.01

Soil Moisture 0.065 0.005Atmosphere 0.013 0.001

Streams and Rivers 0.0017 0.0001Biosphere 0.0006 0.00004

Table 1.1: Water at the Earth's surface

Reservoir Average Residence Time

Glaciers 20 to 100 years

Seasonal Snow Cover 2 to 6 monthsSoil Moisture 1 to 2 months

Groundwater: Shallow 100 to 200 years

Groundwater: Deep 10,000 years

Lakes 50 to 100 years

Rivers 2 to 6 months

Table 1.2: Typical residence times of water found in various reservoirs

Hydrology, as discussed earlier, is the study of the movement and distribution of water

throughout the Earth, and thus addresses both the hydrologic cycle and water resources.Many processes work together to keep Earth's water moving in a cycle. There are five

processes at work in the hydrologic cycle: condensation, precipitation, infiltration, runoff,

and evapotranspiration. These occur simultaneously and, except for precipitation,

continuously. Water vapour condenses to form clouds, which result in precipitation when the

conditions are suitable. Precipitation falls to the surface and infiltrates the soil or flows to the

ocean as runoff. Surface water (e.g., lakes, streams, oceans, etc.), evaporates, returning

moisture to the atmosphere, while plants return water to the atmosphere by transpiration.

The water cycle- technically known as the hydrologic cycle- is the circulation of water

within the earth's hydrosphere, involving changes in the physical state of water betweenliquid, solid, and gas phases. The hydrologic cycle refers to the continuous exchange of water

between atmosphere, land, surface and subsurface waters, and organisms. In addition to

storage in various compartments (the ocean is one such compartment); the multiple cycles

that make up the earth's water cycle involve five main physical actions: evaporation,

precipitation, infiltration, runoff, and subsurface flow

1.3.1. Evaporation It occurs when radiant energy from the sun heats water, causing the

water molecules to become so active that some of them rise into the atmosphere as vapour. It

is the transfer of water from bodies of surface water into the atmosphere. This transfer entails


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a change in the physical nature of water from liquid to gaseous phases. Along with

evaporation can be counted transpiration from plants. Thus, this transfer is sometimes

referred to as evapotranspiration. About 90% of atmospheric water comes from evaporation,

while the remaining 10% is from transpiration. Transpiration occurs when plants take in

water through the roots and release it through the leaves, a process that can clean water byremoving contaminants and pollution. Evapotranspiration is water evaporating from the

ground and transpiration by plants. Evapotranspiration is also the way water vapour re-enters

the atmosphere (Figure 1.2).

Fig 1.2: Evaporation ProcessSelf-check Exercise 2

What are the components of evapotranspiration?Note: Please proceed after answering the question

Do not write full sentences or statements; instead use words or phrases.

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1.3.2. Precipitation

In cold air way up in the sky, rain clouds will often form. Rising warm air carries water

vapor high into the sky where it cools, forming water droplets around tiny bits of dust in the

air.Some vapor freezes into tiny ice crystals which attract cooled water drops. The drops

freeze to the ice crystals, forming larger crystals we call snowflakes. When the snowflakes

become heavy, they fall. When the snowflakes meet warmer air on the way down, they melt

into raindrops. In tropical climates, cloud droplets combine together around dust or sea salt

particles. They bang together and grow in size until they're heavy enough to fall (Figure 1.3).

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Fig 1.3: Precipitation

Look at the figure above. Sometimes there is a layer of air in the clouds that is above

freezing, or 32 F. Then closer to the ground the air temperature is once again below

freezing. Snowflakes partially melt in the layer of warmer air, but then freeze again in the

cold air near the ground. This kind of precipitation is called sleet. It bounces when it hits theground.If snowflakes completely melt in the warmer air, but temperatures are below freezing

near the ground, rain may freeze on contact with the ground or the streets. This is called

freezing rain, and a significant freezing rain is called an ice storm. Ice storms are extremely

dangerous because the layer of ice on the streets can cause traffic accidents. Ice can also

build up on tree branches and power lines, causing them to break and our lights to go out.

There is another kind of precipitation that comes from thunderstorms called hail.

1.3.3. Infiltration

Under some circumstances precipitation actually evaporates before it reaches the

surface. More often, though, precipitation reaches the Earth's surface, adding to the surfacewater in streams and lakes, or infiltrating the A portion of the precipitation that reaches the

Earth's surface seeps into the ground through the process called infiltration.

Infiltration into the ground is the transition from surface water to groundwater. The

infiltration rate will depend upon soil or rock permeability as well as other factors. Infiltrated

water may reach another compartment known as groundwater (i.e., an aquifer). Groundwater

tend to move slowly, so the water may return as surface water after storage within an aquifer

for a period of time that can amount to thousands of years in some cases. Water returns to the

land surface at lower elevation than where it infiltrated, under the force of gravity or gravity

induced pressures.1.3.4. Runoff

The amount of water that infiltrates the soil varies with the degree of land slope, the

amount and type of vegetation, soil type and rock type, and whether the soil is already

saturated by water. The more openings in the surface (cracks, pores, joints), the more

infiltration occurs. Water that doesn't infiltrate the soil flows on the surface as runoff.

Precipitation that reaches the surface of the Earth but does not infiltrate the soil is called

runoff. Runoff can also come from melted snow and ice. Also it includes the variety of ways

by which land surface water moves down slope to the oceans. Water flowing in streams and


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rivers may be delayed for a time in lakes. Not all precipitated water returns to the sea as

runoff; much of it evaporates before reaching the ocean or reaching an aquifer.

1.3.5 Subsurface Flow

Surface flow incorporates movement of water within the earth, either within the recharge

zone or aquifers. After infiltrating, subsurface water may return to the surface or eventuallyseep into the ocean.

Self-check Exercise 3What are the components of hydrological cycle?

Note: Please proceed after answering the questionDo not write full sentences or statements; instead use words or phrases.------------------------------------------------------------------------------------------------------------

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1.4 LET US SUM UP

The main sources of water include rainwater, surface water and groundwater.The

distribution of water varies as per its locations. Water also exists on earth as a solid, liquid or

gas, oceans, rivers, clouds, and rain, all of which contain water, are in a frequent state of

change.

Hydrologic Cycle recycles the earth's valuable water supply. The sun is the energy that

powers this remarkable process. Its energy in the form of light, and heat causes water to

evaporate from oceans, rivers, lakes and even puddles. Warm air currents rising from theearth's surface lift this water vapour up into the atmosphere.

When the air currents reach the cooler layers of the atmosphere, the water vapour

condenses around and clings on to fine particles in the air. This step is called condensation.

When enough vapours attach itself to tiny pieces of dust, pollen or pollutants, it forms a

cloud. As the air gets more and more moist, the droplets that form the clouds grow larger and

larger. Eventually they will get so big that the swirling atmospheric winds can no longer hold

them up. The droplets then fall from the sky as precipitation. Precipitation can be in the form

of rain, snow, sleet or hail depending on other atmospheric conditions such as temperature.

Some of the precipitation will be absorbed into the ground. This is called infiltration.

Once in the ground, the water can join the earth's groundwater supply. This is one of the

world's largest storehouses of water. The water could also be absorbed from the ground by

the roots of plants.

1.5 LESSON END ACTIVITIES

1. Visit the lentic and lotic water bodies in and around your area and take an account ofit.

2. Take a survey about the primary sources of water in your area.


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LESSON 2: PHYSICO-CHEMICAL PROPERTIES OF WATER

CONTENTS

2.0 Aim and Objectives

2.1. Physico Chemical Properties of Water2.2. Physical Properties of Water

2.3. Chemical Properties of Water2.4. Composition of Water

2.4.1 Sea Water

2.4.2 Composition of Rain and Snow2.4.3 Composition of Rivers and Lakes

2.5. Water Hardness2.5.1. Causes of Hard Water2.5.2. Identifying Hard Water

2.5.3. Types of Water Hardness

2.5.4 Temporary Hardness2.5.5 Permanent Hardness

2.6. Conventional Water Softening2.6.1. Water Softening Process

2.6.2. Advantages and Disadvantages of Water Softening2.7 Let Us Sum Up

2.8 Lesson end Activities2.9 Points for Discussion2.10 Check your Progress Model Answers

2.11 References

2.0 AIM AND OBJECTIVES

The main aim of this lesson is to study the general properties of the water. The following

objectives are

To study the physico-chemical properties of the water,

To study the components and composition of the water, and

To study the water hardness and water softening processes.

2.1. PHYSICO CHEMICAL PROPERTIES OF WATER

Every water analysis, or set of analyses, tells us a story: where the water comes from,

how old it is, what rocks have dissolved or precipitated, what are the biologic interactions,

and what has been the human impact. These processes give clue to know various physico-chemical properties of water.

2.2. PHYSICAL PROPERTIES OF WATER

We live on a planet that is dominated by water. More than 70% of the Earth's surface is

covered with the water molecule. Scientists estimate that the hydrosphere contains about

1.36 billion cubic kilometres of this substance mostly in the form of a liquid (water) which

mostly occupies topographic depressions on the Earth. The second most common form of the

water on our planet is ice. Ifthe entire planet's ice is melted, then the sea- level would rise by

about 70 metres.

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Water, as observed in the previous lesson, is essential for life. Water is the major

constituent of almost all life forms. Most animals and plants contain more than 60% water by

volume. Without water life would probably never have developed on our planet.

Water has a very simple atomic structure. This structure consists of two hydrogen atoms

bonded to one oxygen atom (Figure 2.1). The nature of the atomic structure of water causesits molecules to have unique electrochemical properties. The hydrogen side of the water

molecule has a slight positive charge (Figure 2.1). On the other side of the molecule a

negative charge exists. This molecular polarity causes water to be a powerful solvent and is

responsible for its strong surface tension

Fig 2.1: Shows the atomic structure of a water (di-hydrogen monoxide)molecule consists of two hydrogen (H) atoms joined to one oxygen (O) atom.The unique way in which the hydrogen atoms are attached to the oxygen atom

causes one side of the molecule to have a negative charge and the area in theopposite direction to have a positive charge. The resulting polarity of chargecauses molecules of water to be attracted to each other forming the strong

molecular bonds.When the water molecule makes a physical phase change, its molecules arrange

themselves in distinctly different patterns (Figure 2.2). The molecular arrangement taken by

ice (the solid form of the water molecule) leads to an increase in volume and a decrease in

density. Expansion of the water molecule at freezing allows ice to float on top of liquid water.

Now you may be able to appreciate why ice floats on water.

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Fig 2.2: The diagrams illustrate the distinct arrangement patterns of watermolecules as they change their physical state from ice to water to gas. Frozenwater molecules arrange themselves in a particular highly organised rigidgeometric pattern that causes the mass of water to expand and to decrease indensity. It shows a slice through a mass of ice that is one molecule wide. In theliquid phase, water molecules arrange themselves into small groups of joined

particles. The fact that these arrangements are small and allow liquid water tomove and flow. Water molecules in the form of a gas are highly charged withenergy. This high energy state causes the molecules to be always moving andreducing the possibility of bonds between individual molecules from forming.

Table 2.1: Key Physical Properties of Water


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Water has a high specific heat. Specific heat is the amount of energy required tochange the temperature of a substance. Since water has a high specific heat, it canabsorb large amounts of heat energy before it begins to get hot. It also means thatwater releases heat energy slowly when situations cause it to cool. Water's highspecific heat allows for the moderation of the Earth's climate and helps organisms

regulate their body temperature more effectively. Water in a pure state has a neutral pH. Pure water is neither acidic nor basic.

Water changes its pH when substances are dissolved in it. Rain has a naturally acidicpH of about 5.6 because it contains natural derived carbon dioxide and sulfur dioxide.

Water conducts heat more easily than any liquid except mercury. Thischaracteristic features causes large bodies of liquid water like lakes and oceans tohave essentially a uniform vertical temperature profile.

Water molecules exist in liquid form over an important range of temperature

from 0 - 100 Celsius. This range allows water molecules to exist as a liquid in mostplaces on our planet.

Water is a universal solvent. It is able to dissolve a large number of differentchemical compounds. This feature also enables water to carry solvent nutrients inrunoff, infiltration, groundwater flow, and also in living organisms.

Water has a high surface tension. Water is adhesive and elastic, and tends toaggregate in drops rather than spread out over a surface as a thin film. Thisphenomenon also causes water to stick to the sides of vertical structures despitegravity's downward pull. Water's high surface tension allows for the formation ofwater droplets and waves, allows plants to move water (and dissolved nutrients) fromtheir roots to their leaves, and the movement of blood through tiny vessels in thebodies of some animals.

Water molecules are the only substance on Earth that exists in all three physical

states of matter: solid, liquid, and gas. Incorporated in the changes of state aremassive amounts of heat exchange. This feature plays an important role in theredistribution of heat energy in the Earth's atmosphere. In terms of heat beingtransferred into the atmosphere, approximately 75 per cent of this process isaccomplished by the evaporation and condensation of water.

The freezing of water molecules causes their mass to occupy a larger volume.

When water freezes it expands rapidly adding about 9% by volume. Fresh water has amaximum density at around 4 Celsius. Water is the only substance on this planetwhere the maximum density of its mass does not occur when it becomes solidified.

Self-check Exercise 1

What are the important physical properties of water?


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2.3. CHEMICAL PROPERTIES OF WATER

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Water is composed of one atom of oxygen with two atoms of hydrogen. The hydrogen

atoms are 'attached' to one side of the oxygen atom, resulting in a water molecule having a

positive charge on the side where the hydrogen atoms are and a negative charge on the other

side, where the oxygen atom is. Since opposite electrical charges attract, water molecules

tend to attract each other, making water kind of'sticky.' One side with the hydrogen atoms(positive charge) attracts the oxygen side (negative charge) of a different water molecule.

All these water molecules attracting each other mean they tend to clump together. This is

why water drops are, in fact, drops, if it was not for some of Earth's forces, such as gravity, a

drop of water would be ball shaped - a perfect sphere. Even if it does not form a perfect

sphere on Earth, we should be happy that water is sticky.

Water is called the 'universal solvent' because it dissolves more substances than any

other liquid. This means that wherever water goes, either through the ground or through our

bodies, it takes along valuable chemicals, minerals, and nutrients.

2.4. COMPOSITION OF WATER

2.4.1. Sea Water

The oceans account for 97.13% of the world's water, and can be generalized asa 1.1 molar solution of solutes with the averagecomposition of:

The composition of seawater varies with location and depth, withhigher total solutes found in colder polar waters, and with largechanges in non-conservative elements with depth due to biologicalprocesses.

Table 2.2: Composition of Sea Water

2.4.2. Composition of Rain and Snow


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The chemistry of rain and snow is highly variable, and reflect multiple inputsfrom the atmosphere. Determining the composition of rain and snow is afundamental step in evaluating the reaction path certain water has taken, andrain or snow should never be assumed to be simply distilled water. For some

waters, atmospheric input is the only source for sulphate and chloride.

In some areas, such as the New England and Norway, atmosphericcontamination by acid gases results in extremely low pH rain water,significant input of sulphate, nitrate, and chloride, and the secondarymobilisation of aluminum in receiving waters, are resulting in Al toxicity infish.

Table 2.3

2.4.3. Composition of Rivers and Lakes

The composition of a river, and eventually a lake, is a reflection of fourinputs: atmospheric input of gases and solutes, biologic processes, dischargeof groundwater, and local interactions with mineral components in the soil orstream bed.

At baseflow, the water in a gaining river is derived from groundwater,so the composition of the river is really a reflection of the aquifer, while for a

losing stream the reverse holds - the composition of the shallow groundwaterreflects the river, for example an alluvial aquifer.

The composition of a river is a dynamic thing, with concentrationsgenerally (but not always) increasing down stream, but pH generallyincreasing.

Self-check Exercise 2What are the important chemical properties of water?


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2.5.WATER HARDNESS


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Hard water occurs when excess minerals in the water create certain problems. While

these water problems can be frustrating, water hardness is not a safety issue. Hard water is

safe for drinking, cooking, and other household uses.

Hard water can cause several problems for consumers including decreased life of

household plumbing and water-using appliances, increased difficulty in cleaning andlaundering tasks, decreased efficiency of water heaters, and white/chalky deposits on items

such as plumbing, tubs, sinks, and pots and pans.

2.5.1. Causes of Hard Water

Approximately 22 percent of the earths fresh water is groundwater, and naturally, as it

flows through soil and rock, it picks up minerals. Hard water results when an excessive

amount of calcium and magnesium are present. Total hardness is measured in milligrams per

litre (mg/l). Sometimes hardness is measured in parts per million (ppm). Parts per million

(ppm) measures the unit(s) of a substance for every one million units ofwater. Milligrams per

litre (mg/l) and parts per million (ppm) are roughly equal in water analysis. When conductingchemical analysis, laboratories usually measure hardness minerals in milligrams per liter

(mg/l).

Table 2.4

2.5.2. Identifying Hard Water

Decreased cleaning capabilities of soaps and detergents, resulting in dingy laundry

and reduced life of fabrics.

Increased buildup of scale on plumbing fixtures and cooking utensils.

Film left on the body resulting in dry skin and dull, limp hair.

Soap scum on bathtubs, shower tiles, and basins.

Increased water heating costs due to scale buildup and mineral deposits, and more

frequent replacement of hot water heating elements.


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Clogged pipes or appliances resulting in reduced water flow and increased repairs.

2.5.3. Types of Water HardnessTemporary Hardness

This refers to hardness whose effects can be removed by boiling the water in an open

container. Such waters have usually percolated though limestone formations and contain

bicarbonate HCO3 along with small amounts of carbonate CO3

2 as the principal negative

ions. Boiling the water promotes the reaction

2 HCO3 CO3

2 + CO2

by driving off the carbon dioxide gas. The CO32 reacts with Ca2+ or Mg2+ ions, to form

insoluble calcium and magnesium carbonates which precipitate out. By tying up the metal

ions in this way, the amounts available to form soap scum are greatly reduced.

Permanent Hardness

Waters that contain other anions such as chloride or sulphate cannot be remediated by

boiling, and are said to be 'permanently' hard. The only practical treatment is to remove all

the ions, normally by the method described below.


How do you identify the water hardness?Note: Please proceed after answering the question

Do not write full sentences or statements; instead use words or phrases.

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2.6. CONVENTIONAL WATER SOFTENING

Most conventional water-softening devices depend on a process known as ion-exchange

in which 'hardness' ions trade places with sodium and chloride ions that are loosely bound to

an ion-exchange resinor azeolite

Fig 2.3: The above diagram depicts a negatively-charged zeolite to which[positive] sodium ions are attached. Calcium or magnesium ions in the water displace

sodium ions, which are released into the water. In a similar way, positively-chargedzeolites bind negatively-charged chloride ions (Cl), which get displaced bybicarbonate ions in the water. As the zeolites become converted to their Ca2+ andHCO3

forms they gradually lose their effectiveness and should be regenerated. This


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is accomplished by passing a concentrated brine solution though them, causing theabove reaction to be reversed. It is one of the drawbacks of this process: most of thesalt employed in the regeneration process gets flushed out of the system and is usuallyreleased into the soil or drainage system something that can have damagingconsequences to the environment, especially in arid regions. For this reason, many

jurisdications prohibit such release, and require users to dispose of the spent brine atan appropriate approved site or to use a private company.

2.6.1. Water Softening Process

A water softener, also called an ion exchange unit, will effectively accomplish the latter

option.

Ion Exchange.Because water softening devices have long been available in the water

treatment industry, the technology is highly developed and in most cases works well to

reduce the hardness level. How does ion exchange work? The physical and chemical process

filters the water through an exchange media known as resin or zeolite. System, the resin is asynthetic or natural, sand- like material coated with positively charged sodium ions. As the

calcium and magnesium dissolves into positively charged ions, an ion exchange environment

is created. The water flows through the unit while the resin releases its sodium ions and

readily trades them for the calcium and magnesium ions. The water flowing out of the device

is now considered soft.

Regeneration. The resin is not an inexhaustible exchange site. When all the sodium

exchange sites are replaced with hardness minerals, the resin is spent and will no longer

soften water. At this point, the water softener will need to be run on an alternate cycle called

regeneration. During this cycle, resin is backwashed with a salt solution. The brine is reverseflushed through the system taking with it the calcium and magnesium ions that had been

adsorbed on the resin. Once backwashing is complete, the softener can be returned to use.

Some water softeners will automatically switch to the operation cycle. Others have a manual

operating system.

The following figure shows both cycles of the water softening procession exchange

and regeneration.


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Fig 2.4: Water Softening Process

Kinds of Softeners.Although many models of ion exchange units exist on the market,

all essentially perform the same with minor differences in extra features, flow rates, etc.

Nearly all softeners fall into one of two categories. Timed models have programmable time

clocks that will regenerate on a predetermined schedule and then return to service. These

work well for households that are on regular water-using cycles but will waste more waterand salt because they regenerate whether the resin needs it or not. Demand-control models,

with either electrical or mechanical sensors, usually regenerate after so many litres of water

have been softened. Such models are convenient if have a fluctuating water use schedule.

Maintenance. No matter which model you choose, all water softeners need to be

properly maintained. The brine solution must be mixed and stored in the brine tank. Periodic

clogging of the resin also requires special attention. For example, if the raw water supply is

turbid it may clog the resin with mud and clay. Sometimes, normal backwashing with water

will solve this problem. If not, slowly stir the resin during the backwash cycle to help break

up the material. Likewise, bacteria and fungi also form mats in the resin that reduce itseffectiveness. Disinfecting the water prior to softening or periodically cleaning the softener

with chlorine bleach will eliminate these nuisances. However, read the manufacturers

instructions before adding any chemicals to the unit. Iron fouling is another common

maintenance problem for water softeners. Although colourless, reduced iron will be removed

by the unit, red-oxidized iron (iron that has been exposed to air or chlorine) will clog the

resin. Filtration prior to softening insures that oxidized iron is not processed in the softener. If

the resin has already been fouled, commercial cleaners are available. Again, it is advisable to

check the manufacturers instructions for special precautions.


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In some instances, resins can not be washed of contaminants and will need to be

replaced (This should not be the case if the resin is periodically regenerated and maintained.)

Consult your water softener dealer for information on resin replacement.

Costs.Water softening costs depend on factors such as installation, maintenance fees,

and size of the unit. You can also expect that with more convenience features, the price of theunit will increase.

2.6.2. Advantages and Disadvantages of Water Softening

The water treatment industry is gaining importance and momentum in India, especially

in Tamil Nadu, the concept of water softening has often been misconstrued as a purifying,

cleansing or conditioning process. This is due largely to exaggerated advertising and, in part,

to consumer misconceptions about water treatment. The reality is that water softening simply

removes hardness minerals and eliminates problems that are a nuisance and not a threat to

human health. The decision 'to soften or not to soften' is a matter of personal preference -not

necessity. However, water softening does have advantages, and disadvantages that make thisdecision a significant one.

Advantages. Most consumers would agree that hard water leaves scales on pots, soap

films on skin, and detergent curds in the washing machine. More importantly, scales can also

buildup on hot water heaters and decrease their useful life. Soap film and detergent curds in

bathtubs and appliances indicate that you are not getting the maximum cleaning action from

these products. Soft water not only eliminates these nuisances but also protects appliances

and saves cleaning time.

There are other advantages to water softening, as well. It is a well developed technology

that has been used in homes for several years. The simple technology of softening makes it

easy to bypass toilets and outdoor faucets. Softening systems are adaptable for mixing

softened and unsoftened water to produce a lower hardness level.

Disadvantages.The major disadvantage to water softening is the potential health risks for

people on low sodium diets. Maintenance is another consideration. When purchase models with

special features that do everything but add the salt, we have to pay for each additional feature.

The tradeoff will be cost for convenience and we have no long-term guarantee that the special

feature will not fail. Depending on the water source, we have to filter turbid water or disinfect

bacteria-laden waterall before it even reaches the softening unit.


What are all the elements of water softening processes?Note: Please proceed after answering the question

Do not write full sentences or statements; instead use words or phrases.------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------


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2.11 REFERENCES

Alagappa Moses. A andAlice Emerenshiya. C

-Advances in Environmental Sciences, GEMS,Tiruchirappalli, 2007

Anil Kumar De - Environmental Chemistry, 1997Raghunath., H. M

-

Hydrology, Mohindar Singh Sejwal for Wiley Eastern

Limited, New Delhi, India. (1988),Dhruva Narayana, V.V.,G. Sastry, and U.S.Patnaik

-Watershed Management

Division of Water Fact

Sheet-

The Hydrologic Cycle, Ohio Department of Natural

Resources, Fact sheet 93 18.Kumaraswamy. K., A.Alagappa Moses and M.

Vasanthy

-Environmental Studies (A Text Book for all Under GraduateCourses) Bharathidasan University, Tiruchirappalli.Publication No. 45. p138 142. 2004..

Metcalf and Eddy-

Wastewater Engineering Treatment and Reuse. Tata

McGraw Hill Edition, New Delhi, 2003.Stanly Manahan

-Environmental Chemistry, Mc Graw Hill Publishingcompany, 1999

Gilbert M. Masters-

Introduction to Environmental Science and Engineering,Prentice Hall of India Private Limited, New Delhi, 1998

Sharma. B. K.-

Environmental Chemistry, Krishna Prakashan Media (p)Ltd, Meerut. 2000

Web site - www.who.int/water_sanitation_health/dwq/gdwq3rev/en/

Web site - http://www.wxdude.com/page3.html/Web site http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/evap.rx

ml

Web site http://www.physicalgeography.net/fundamentals/8a.htmlWeb site http://resources.cas.psu.edu/WaterResources/pdfs/WaterSof

tening.pdfWeb site http://www.ext.vt.edu/pubs/housing/356 -490/356-490.pdf

http://www.clicktoconvert.com/http://www.ext.vt.edu/pubs/housing/356-490/356-490.pdfhttp://www.ext.vt.edu/pubs/housing/356-490/356-490.pdfhttp://www.ext.vt.edu/pubs/housing/356-490/356-490.pdfhttp://www.ext.vt.edu/pubs/housing/356-490/356-490.pdfhttp://www.ext.vt.edu/pubs/housing/356-490/356-490.pdfhttp://resources.cas.psu.edu/WaterResources/pdfs/WaterSoftening.pdfhttp://resources.cas.psu.edu/WaterResources/pdfs/WaterSoftening.pdfhttp://www/http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/evap.rxmlhttp://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/evap.rxmlhttp://www.who.int/water_sanitation_health/dwq/gdwq3rev/en/http://www.who.int/water_sanitation_health/dwq/gdwq3rev/en/http://www.who.int/water_sanitation_health/dwq/gdwq3rev/en/

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LESSON 3: WATER QUALITY AND STANDARDS

CONTENTS

3.0. Aims and Objectives

3.1. Introduction3.2. Water Quality

3.3. Water Temperature3.4. pH3.5. Specific Conductance

3.6. Turbidity3.7. Dissolved Oxygen

3.8. Hardness3.9. Suspended Sediment3.10 Potable Water Quality

3.10.1. Impurities in Water

3.10.2. Raw Water Classifications3.10.3. Treated Water Classifications3.10.4. Physical Quality3.10.5. Chemical Quality

3.10.6. Microbiological Quality3.11. Water Quality Standards

3.11.1. Standards for Potable and Safe water3.12 Let Us Sum Up3.13 Lesson End Activities

3.14 Points for Discussion3.15 Check your Progress Model Answers

3.16 References

3.0. AIMS AND OBJECTIVES

The main aim of this lesson is to discuss the different types of water qualities like

physical, chemical and microbial aspects and the objectives are

To study the physical, chemical and microbial qualities of the water,

To learn the different types of procedures to analyze the parameters of water qualities,and

To learn different water quality standards and guidelines for drinking, agricultural and

industrial purposes.3.1. INTRODUCTION

Water quality is a term used here to express the suitability of water to sustain various

uses or processes. Any particular use will have certain requirements for the physical,

chemical or biological characteristics of water; for example limits on the concentrations of

toxic substances for drinking water use, or restrictions on temperature and pH ranges for

water supporting animals. Consequently, water quality can be defined by a range of variables

which limit the water. Although many uses have some common requirements for certain

variables, each use will have its own demands and influences on water quality.


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Quantity and quality demands of different users will not always be compatible, and the

activities of one user may restrict the activities of another, either by demanding water of a

specific quality outside the range required by the other user or by lowering quality during use

of the water. Efforts to improve or maintain a certain water quality often compromisebetween the quality and quantity demands of different users. There is an increasing

recognition that natural ecosystems have a legitimate place in the consideration of options for

water quality management. This is both for their intrinsic value and because they are sensitive

indicators of changes or deterioration in overall water quality, providing a useful addition to

physical, chemical and other information.

3.2.WATER QUALITY

The composition of surface and under groundwater is dependent on natural factors

(geological, topographical, meteorological, hydrological and biological) in the drainage basin

and varies with seasonal differences in runoff volumes, weather conditions and water levels.

Large natural variations in water quality may, therefore, be observed even where only a

single watercourse is involved. Human intervention also has significant effects on water

quality. Some of these effects are the result of hydrological changes, such as building of

dams, draining of diversion of waste waters. More obvious are the polluting activities, such

as the discharge of domestic, industrial, urban and other wastewaters into the watercourse

(whether intentional or accidental) and the spreading of chemicals on agricultural land in the

drainage basin.

Water quality is affected by a wide range of natural and human influences. The most

important of the natural influences are geological, hydrological and climatic, since these

affect the quantity and the quality of water available. Their influence is generally higher

when available water quantities are low and maximum use is to be made of the limited

resource; for example, high salinity is a frequent problem in arid and coastal areas. If the

financial and technical resources are available, seawater or saline groundwater can be

desalinated but in many circumstances this is not economically feasible. Thus, although water

may be available in adequate quantities, its unsuitable quality limits the uses that can be made

of it.

Although the natural ecosystem is in harmony with natural water quality, any significantchanges to water quality will usually be disruptive to the ecosystem. The effects of human

activities on water quality are both widespread and varied in the degree to which they disrupt

the ecosystem and/or restrict water use. Pollution of water by human activities, for example,

is attributable to only one source, but the reasons for this type of pollution, its impacts on

water quality and the necessary remedial or preventive measures are varied. Faecal pollution

may occur because there are no community facilities for waste disposal, because collection

and treatment facilities are inadequate or improperly operated, or because on-site sanitation

facilities (such as latrines) drain directly into aquifers.


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The effects of faecal pollution vary appreciably in space and time. In developing

countries intestinal disease is the main problem, while organic load and eutrophication may

be of greater concern in developed countries (in the rivers into which the sewage or effluent

is discharged and in the sea into which the rivers flow or sewage sludge is dumped). A single

influence may, therefore, give rise to a number of water quality problems, just as a problemmay have a number of contributing influences. Eutrophication results not only from point

sources, such as wastewater discharges with high nutrient loads (principally nitrogen and

phosphorus), but also from diffuse sources such as run-off from livestock feedlots or

agricultural land fertilized with organic and inorganic fertilisers. Pollution from diffuse

sources, such as agricultural runoff, or from numerous small inputs over a wide area, such as

faecal pollution from unsewered settlements, is particularly difficult to control.

The quality of water may be described in terms of the concentration and state (dissolved

or particulate) of some or all of the organic and inorganic material present in the water,

together with certain physical characteristics of the water. It is determined by in situmeasurements and by examination of water samples on site or in the laboratory. The main

elements of water quality monitoring are, therefore, on-site measurements, the collection and

analysis of water samples, the study and evaluation of the analytical results, and the reporting

of the findings. The results of analyses performed on a single water sample are only valid for

the particular location and time at which that sample was taken. One purpose of a monitoring

programme is, therefore, to gather sufficient data (by means of regular or intensive sampling

and analysis) to assess spatial and/or temporal variations in water quality.

3.3. WATER TEMPERATURE

Water temperature is not only important to fisherman and industries, but also to the

growth of fish and algae. A lot of water is used for cooling purposes in power plants that

generate electricity. They need cool water to start with, and they generally release warmer

water back to the environment. The temperature of the released water can affect downstream

habitats. Temperature also can affect the ability of water to hold oxygen as well as the ability

of organisms to resist certain pollutants.

3.4. pH

The pH is a measure of how acidic/basic a water sample is. The range goes from 0 - 14,

with 7 being neutral. The pH of less than 7 indicates acidity, whereas a pH of greater than 7

indicates a base. The pH is really a measure of the relative amount of free hydrogen and

hydroxyl ions in the water. Water that has more free hydrogen ions is acidic, whereas water

that has more free hydroxyl ions is basic. Since pH can be affected by chemicals in the water,

pH is an important indicator of water that is changing chemically. The pH is reported in

"logarithmic units," like the Richter scale, which measures earthquakes. Each number

represents a 10-fold change in the acidity/basicness of the water. Water with a pH of 5 is ten

times more acidic than water having a pH of six.

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Pollution can change a water's pH, which in turn can harm animals and plants living in

the water. For instance, water coming out of an abandoned coal mine can have a pH of 2,

which is very acidic and would definitely affect any fish and other micro organisms. By using

the logarithm scale, this mine-drainage water would be several hundred times more acidic

than neutral water so stay out of abandoned mines.

3.5. SPECIFIC CONDUCTANCE

Specific conductance is a measure of the ability of water to conduct an electrical current.

It is highly dependent on the amount of dissolved solids (such as salt) in the water. Pure

water, such as distilled water, will have a very low specific conductance, and sea water will

have a high specific conductance. Rainwater often dissolves airborne gasses and airborne

dust while it is in the air, and thus often has a higher specific conductance than distilled

water. Specific conductance is an important water-quality measurement because it gives a

good idea of the amount of dissolved material in the water.

3.6. TURBIDITY

Turbidity is the amount of particulate matter that is suspended in water. Turbidity

measures the scattering effect that suspended solids have on light: the higher the intensity of

scattered light, the higher the turbidity. Material that causes water to be turbid include:

clay

silt

finely divided organic and inorganic matter

soluble coloured organic compounds

plankton microscopic organisms

Turbidity makes the water cloudy or opaque. Turbidity is measured by shining a light

through the water and is reported in Nephelometric Turbidity Units (NTU). During periods of

low flow (base flow), many rivers are a clear green colour, and turbidities are low, usually

less than 10 NTU. During a rainstorm, particles from the surrounding land are washed into

the river making the water a muddy brown colour, indicating water that has higher turbidity

values. Also, during high flows, water velocities are faster and water volumes are higher,

which can more easily stir up and suspend material from the stream bed, causing higher

turbidities.

Turbidity can be measured in the laboratory and also on-site in the river. A handheld

turbidity meter measures turbidity of a water sample. The meter is calibrated using standard

samples from the meter manufacturer. The picture with the three glass vials shows turbidity

standards of 5, 50, and 500 NTUs. Once the meter is calibrated to correctly read these

standards, the turbidity of a water sample can be taken.

3.7. DISSOLVED OXYGEN

Although water molecules contain oxygen atom, this oxygen is not what is needed by

aquatic organisms living in natural waters. A small amount of oxygen, upto about ten


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molecules of oxygen per million of water, is actually dissolved in water. This dissolved

oxygen is breathed by fish and zooplankton and is needed by them to survive.

Rapidly moving water, such as in a mountain stream or large river, tends to conta in a lot

of dissolved oxygen, while stagnant water contains little. Bacteria in water can consume

oxygen as organic matter decays. Thus, excess organic material in the tanks, lakes and riverscan cause an oxygen-deficient situation to occur. Aquatic life can have a hard time in

stagnant water that has a lot of rotting, organic material in it, especially in summer, when

dissolved-oxygen levels are at a seasonal low.

3.8. HARDNESS

The amount of dissolved calcium and magnesium in water determines its hardness. If

some one live in an area where the water is soft, then you may never have even heard of

water hardness. But, ifone live, where the water is relatively hard, may notice that it is

difficult to get lather up when washing your hands or clothes. And, industries in these area

might have to spend money to soften their water, as hard water can damage equipment. Hard

water can even shorten the life of fabrics and clothes.

3.9. SUSPENDED SEDIMENT

Suspended sediment is the amount of soil moving along in a stream. It is highly

dependent on the speed of the water flow, as fast-flowing water can pick up and suspend

more soil than calm water. During storms, soil is washed from the stream banks into the

stream. The amount that washes into a stream depends on the type of land in the river's

watershed and the vegetation surrounding the river.

If land is disturbed along a stream and protection measures are not taken, then excess

sediment can harm the water quality of a stream. These bunds and fences are supposed to trap

sediment during a rainstorm and keep it from washing into a stream, as excess sediment can

harm the creeks, rivers, lakes, and reservoirs.

Sediment coming into a reservoir is always a concern; once it enters it cannot get out -

most of it will settle to the bottom. Reservoirs can silt in if too much sediment enters them.

The volume of the reservoir is reduced, resulting in less area for water storage for agriculture

as well as reducing the power-generation capability of the power plant in the dam.

Self-check Exercise 1What factors affect the surface and groundwater quality of an area?


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3.10 POTABLE WATER QUALITY

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Potable water must be free of anything that would degrade human performance. Further,

it should not damage the materials used in its transportation and storage. Potable water must

be suitable for maintaining human health (personal hygiene and medical treatment). Water

quality standards give a basis for selecting or rejecting water intended for human use. These

standards provide minimum accepted values for safeguarding human health.3.10.1. Impurities in Water

As water goes through the hydrologic cycle, it gathers many impurities. Dust, smoke,

and gases fill the air and can contaminate rain, snow, hail, and sleet. The rain water picks up

silt, chemicals, and disease organisms. As it enters the earth through seepage and infiltration,

some of the suspended impurities may be filtered out. However, other minerals and chemicals

are dissolved and carried along. As groundwater it may contain disease organisms as well as

harmful chemicals. In addition to the impurities in water resulting from infiltration, many are

contributed by an industrialized society. The garbage, sewage, industrial waste, pesticides

etc., are all possible contaminants of raw water. Impurities in raw water are either suspendedor dissolved. Suspended impurities include diseases organisms, silt, bacteria, and algae. They

must be removed or destroyed before the water is consumed. Dissolved impurities include

salts, (calcium, magnesium, and sodium), iron, manganese, and gases (oxygen, carbon

dioxide, hydrogen sulphide, pH and nitrogen). These impurities must be reduced to levels

acceptable for human consumption.

3.10.2. Raw Water Classifications

Water is classified as fresh, brackish, or salt water (seawater) based on the concentration

of TDS (Total Dissolved Solids). Fresh water has a TDS concentration of less that 1,500

ppm. Brackish water is high in minerals and has a TDS concentration between 1,500 ppm and16,000 ppm. Salt water has a TDS concentration greater than 15,000 ppm.

Generally, groundwater (subsurface) has less chemical or biological contaminants than

surface water, provided reasonable care is exercised in the selection of the well site. Harmful

micro organisms are usually reduced to tolerable levels by passage through the soil.

3.10.3. Treated Water ClassificationsPalatable Water

Palatable water is water that is pleasing in appearance and taste. It is significantly free

from colour, turbidity, taste, and odour. It should also be cool and aerated.

Potable Water Quality StandardsQuality standards for treated water reflect the values of substances allowed in potable

water. Standards exist to measure the physical, chemical, microbiologic, and radiologic

quality of water and to test for the presence of chemical agents.

3.10.4. Physical Quality

The principal physical characteristics of water are colour, odour and taste, turbidity, and

temperature. These characteristics and their related quality standards are described below.

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Colour-Colour in water is derived from coloured substances, such as vegetable matter,

dissolved from roots and leaves, from humus, or from inorganic compounds such as iron and

manganese salts. The colour standard is designed to make drinking water more palatable.

Odour and Taste -There is no set standards for odour and taste as there are no specific

tests for these. Odour and taste found in water are most commonly caused by algae,decomposed organic matter, dissolved gases, or industrial waste.

Turbidity - Turbidity refers to a muddy or unclear condition of water caused by

suspended clay, silt, organic and inorganic matter, and plankton and other microorganisms.

The turbidity standard was established to improve the efficiency of disinfection by reducing

particles to which micro organisms could attach.

Temperature -Warm water tastes flat. Cooling water suppresses odours and tastes and

makes it more palatable. Temperature also effects the chlorination and purification of water.

Disinfection takes longer when water is colder, and purification capacity is reduced with

reverse osmosis treatment equipment. Water having physical characteristics exceeding the

limits or making it less palatable should not be used for drinking. Otherwise, reduced

consumption and increased risk of dehydration may result. When water of low physical

quality has not been used, the appropriate command level will make that decision based on

medical recommendations.

3.10.5. Chemical Quality

The chemical quality of water depends on the chemical substances it contains. These

substances include TDS, chlorides, sulphates and other ions. The chemical quality of water

involves its hardness, alkalinity, acidity, and corrosiveness. Chemical substances having an

adverse health effect have established standards that will not be exceeded without medical

approval.

Potential Hydrogen -The pH is a measure of the acidic or alkaline nature of water. It is

technically defined as the negative logarithm of the hydrogen ion concentration. It ranges

from 0 to 14 and pH of 7 is neutral. The pH influences the corrosiveness of the water, the

amount of chemicals needed for proper disinfection, and the ability of an analyst to detect

contaminants. Water with a pH below 7 is regarded as acidic while that with a pH above 7 is

regarded as alkaline. The pH standard was established to ensure effective purification and

disinfection.

Arsenic

Arsenic can be present in natural water sources in a wide range of concentrations. It can

come from either natural or industrial sources. Ingestion of low concentrations of arsenic can

cause nausea, vomiting, abdominal pain, or nerve damage.

Chloride

Chloride exists in most natural waters. It is the main anion found in seawater. Chloride

comes from natural salt deposits, domestic and industrial waste, and agricultural runoff. Even

in low concentrations, chloride can produce an objectionable taste in water. The chloride

standard ensures that potable water is also palatable.


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Calcium, Magnesium and Hardness

Calcium and magnesium in drinking water, is an important parameter is to be taken into

account: water hardness, even if this term is incorrect and obsolete from a strictly chemical

point of view. That is to say that both of these elements largely have not been analysed

individually in drinking water in the past, but just non-specifically in summary as hardness.This approach was applied in many studies focused on health effects of this water factor.

Since the definition of water hardness is approached either analytically or

technologically, it was not and still has not been defined in a unified manner, and as with

other parameters, multiple definitions have been available and multiple units have been used

to express it (German, French, and English degrees; equivalent CaCO3 or CaO in mg/l).

Initially, water hardness was understood to be a measure of the capacity of water to

precipitate soap, which is in practice the sum of concentrations of all polyvalent cations

present in water (Ca, Mg, Sr, Ba, Fe, Al, Mn, etc.); nevertheless, since the other ions (apart

from Ca and Mg) play a minor role in this regard, later it has been generally accepted thathardness is defined as the sum of the Ca and Mg concentrations.

From the technical point of view, multiple different scales of water hardness were

suggested (e.g. very soft soft medium hard hard very hard). Expectedly, both extreme

degrees (i.e. very soft and very hard) are considered as undesirable concordantly from the

technical and health points of view, but the optimum Ca and Mg water levels are not easy to

determine since the health requirements may not coincide with the technical ones.

Calcium and magnesium presence in waters

Water calcium and magnesium result from decomposition of calcium and magnesium

aluminosilicates and, at higher concentrations, from dissolution of limestone, magnesium

limestone, magnesite, gypsum and other minerals. Anthropogenenic contamination of

drinking water sources with calcium and magnesium is not common but drinking water may

be intentionally supplemented with these elements while treated, as happens with

deacidification of underground waters by means of calcium hydroxide or filtration through

different compounds counteracting acidity such as CaCO3, MgCO3 and MgO, and possibly

also with stabilization of low-mineralized waters by addition of CaO and CO2.

In low- and medium-mineralized underground and surface waters (as drinking waters

are), calcium and magnesium are mainly present as simple ions Ca2+ and Mg2+ , the Ca

levels varying from tens to hundreds of mg/l and the Mg concentrations varying from units to

tens ofmg/l.

Magnesium is usually less abundant in waters than calcium, which is easy to understand

since magnesium is found in the Earths crust in much lower amounts as compared with

calcium. In common underground and surface waters the weight concentration of Ca is

usually several times higher compared to that of Mg, the Ca to Mg ratio reaching up to 10.

Nevertheless, a common Ca to Mg ratio is about 4, which corresponds to a substance ratio of

2.4.



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What is the role of Calcium in defining water hardness?Note: Please proceed after answering the question

Do not write full sentences or statements; instead use words or phrases.------------------------------------------------------------------------------------------------------------

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Sulphates - Sulphates occur naturally in water as the result of dissolution of sulfur-

bearing minerals. Significant concentrations also result from industry sources, such as coal

mine drainage, pulp paper mills, tanneries, textile mills, and domestic waste water. When

ingested, sulphates have a laxative effect. They also can produce a bad taste in water. The

sulphate standard was established to prevent chemically induced diarrhea.

Total Dissolved Solids - The TDS of water is composed of mineral salts and small

amounts of other inorganic and organic substances. The proportion of each constituent is the

result of weathering of rocks found in the drainage basin and of any industrial contributions.Since TDS is composed of chloride, magnesium, sulfate, and other ions, its ingestion in water

has the same effects. Therefore, the TDS standard was established to prevent chemically

induced diarrhea.

Chemical water quality standards are based on the effect the water will have on the

health of living organisms. The effect of a particular chemical substance determines if a limit

is established for that substance. Chemical substances having a negative physical effect will

have a mandatory limit that should not be exceeded. Some substances, such as iron and

manganese, have no significant negative physical effect, but may restrict the use of the water,

such as for the laundering of clothes.

3.10.6. Microbiological Quality

The microbiological quality of potable water shows its potential for transmitting

waterborne diseases. These diseases may be caused by viruses, bacteria, protozoa, or higher

organisms. A microbiological test will reveal the quality of the raw water source and aid in

determining any treatment required. The test is necessary to maintain the quality of the water.

The testing for microorganisms in water is extremely difficult. The number of these

organisms is usually very low, even in a badly polluted water supply, and the test used to find

them is difficult. For these reasons, indicator organisms are used to detect the presence of

contamination. The bacterial organisms used as an indicator of possible contamination aretotal coliform. These organisms occur in large quantities in the intestines of warm-blooded

animals. The presence of any coliform organism in treated potable water is an indication of

either inadequate treatment or the introduction of undesirable materials to the water after

treatment. While the detection of many disease-causing microbes is difficult, the test to detect

a surrogate organism, E. coli, is simple and effective for field use. Because of its relative

simplicity and field adaptability, the membrane filter technique has gained wide acceptance

as the preferred technique for the presumptive determination of the presence of coliform


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organisms in potable water. The microbiological standard was established to ensure

infectious microorganisms would not cause diseases.

3.11. WATER QUALITY STANDARDS

The idea of water quality management is to ensure that water supplied is free from

pathogenic organisms, clear, potable and free from undesirable taste and odour, of reasonable

temperature, either corrosive nor scale forming and free from minerals which could produce

undesirable physiological effect. The establishment of minimum standards of quality for

public water supply is of fundamental importance in achieving this ideal. Standards of quality

from the yardstick with which the quality control of any public water supply has to be

assessed. In India, certain minimum standards have already been prescribed and given here.

3.11.1. Standards for Potable and Safe water

National Drinking Water Mission is an institution which is the in-charge to define the

standards for potable water with respects to their locations. It is defined as the water that is

free from pathogenic microorganisms, poisonous substances, excessive amounts of

minerals and organic matter which would produce undesirable physiological effects. It should

be free from colour, turbidity, taste and odour, of moderate temperature and aerated.

The physical and chemical quality of water should not excess the limits shown in the table

below:

Sl.No. Characteristics * Acceptable ** Cause for

Rejection

1. Turbidity (Units on JTU scale) 2.5 102. Colour (units on platinum-cobalt

scale)

5.0 25

3. Taste and odour Unobjectionable Unobjectionable4. pH 7.0 to 8.5 6.5 to 9.2

5 Total dissolved solids 500 15006 Total hardness (mg/l as CaCO3) 200 600

7 Chlorides (mg/l as Cl) 200 10008 Sulphates (as SO4, mg/l) 200 10009 Fluorides (as F, mg/l) 1.0 1.5

10 Nitrates (as NO3, mg/l) 45 10011 Calcium (as Ca, mg/l) 75 200

12 Magnesium (as Mg, mg/l) 30 15013 Iron (as Fe, mg/l) 0.1 1.014 Manganese (as Mn, mg/l) 0.05 0.5

Table 3.1:Physical and Chemical Standards

Notes* 1. The figure indicated under the column acceptable are the limits upto which the water isgenerally acceptable to the customers.

** 2. Figures in excess of those mentioned under acceptable render the water non-acceptablebut still may be tolerated in the absence of alternative and better source but upto the limitsindicated under column cause for rejection above which the supply will have to be rejected.

(Source : From Document of National Drinking Water Mission)


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Bacteriological Standardsa) Coliform count in any sample of 100 ml should be zero. A sample of water

entering the distribution system that does not conform to this standard callsan immediate investigation into both efficacy of the purification and themethod of sampling.

b) Water in the distribution system shall satisfy all the three criteria indicatedbelow:

- E,Coli count in 100 ml of any sample should be zero- Coliform organisms not more that 10 per 100 ml shall be present in

any sample.- Coliform organisms should not be detectable in 100 ml of