comparison of water harvesting with borehole...

UNIVESITY OF NAIROBI

DEPARTMENT OF CIVIL AND CONSTRUCTION ENGINEERING

COMPARISON OF WATER HARVESTING WITH BOREHOLE

WATER AS ALTERNATIVE SOURCES OF WATER FOR

SYOKIMAU AREA IN MAVOKO MUNICIPALITY

By Auni Mbarak Shebe

F16/29448/2009

A Project submitted as a partial fulfillment for the requirement for

the award of the degree of Bachelor of Science in civil engineering

Supervisor: DR. NDIBA PETER KURIA

2014

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ABSTRACT

The purpose of this study was to compare water harvesting and borehole water as alternative

sources of water for Syokimau area in Mavoko Municipality. This study is accomplished by

determination of water availability, reliability of the sources, the quality of water and assessing the

better alternative source of water in Syokimau.

The availability and reliability of water harvesting was carried out through rainfall analysis for the

area while that of borehole water was carried out by analysis of existing borehole data within

Syokimau. Samples for each of the water source were collected and tested at the Public Health

Engineering Laboratory of the University of Nairobi.

The study showed that the water availability from both sources were sufficient for domestic use.

Boreholes in the area yields an average of 160.9 l/min while water harvesting yields 336.4 m3 of

water for an average roof area of 375 m2. However water harvesting could not be relied upon as

rainfall in the area varies through different seasons. The water quality tests confirmed that water

from both sources met the water quality standards (Guidelines for Drinking-water Quality – WHO,

2011) and therefore is suitable for domestic use.

The borehole water was found to be a better alternative source of water compared to water

harvesting within Syokimau area and therefore the most suitable one for domestic use.

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DEDICATION

This project is lovingly dedicated to my family who have been my constant source of inspiration.

They have given me the drive and discipline to tackle any task with enthusiasm and determination.

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ACKNOWLEDGEMENT

I would like to express my deep gratitude to Dr. P.K Ndiba, my research supervisor, for his patient

guidance, enthusiastic encouragement and useful critiques of this research work. I would also like

to extend my thanks to the technicians of the Public Health Engineering Laboratory of the

University of Nairobi for their help in offering me the resources in carry out experiments for this

research work.

Finally, I wish to thank my family for their support and encouragement throughout my study.

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TABLE OF CONTENT

ABSTRACT ............................................................................................................................. i

DEDICATION......................................................................................................................... ii

ACKNOWLEDGEMENT ...................................................................................................... iii

TABLE OF CONTENT.......................................................................................................... iv

LIST OF FIGURES ............................................................................................................... vii

LIST OF TABLES................................................................................................................ viii

CHAPTER ONE ............................................................................................................................. 1

1.0 INTRODUCTION ................................................................................................................. 1

1.1 Background Information.................................................................................................... 1

1.2 Problem Statement ............................................................................................................. 2

1.3 Objectives .......................................................................................................................... 3

CHAPTER TWO ............................................................................................................................ 4

2.0 LITERATURE REVIEW ...................................................................................................... 4

2.1 WATER HARVESTING .................................................................................................. 4

2.1.1 Water Requirement/Demand ...................................................................................... 4

2.1.2 Rainfall Characteristics ............................................................................................... 5

2.1.3 Catchment Characteristics .......................................................................................... 6

2.1.4 Quantity of Water Available (Run-off) and Storage Requirement ............................. 6

2.1.5 Quality of Water and its Uses ..................................................................................... 8

2.1.6 Sources of Pollution and Treatments of Rainwater Harvesting .................................. 8

2.2 BOREHOLE WATER ....................................................................................................... 9

2.2.1 Extraction and Quantity of Water in Boreholes ........................................................ 10

2.2.2 Storage Requirement for a Water Borehole .............................................................. 10

2.2.3 Borehole Water Quality ............................................................................................ 11

2.2.4 Pollution Sources and Treatment of Borehole Water ............................................... 11

CHAPTER THREE ...................................................................................................................... 13

3.0 METHODOLOGY .............................................................................................................. 13

3.1 Introduction ..................................................................................................................... 13

3.2 Water Demand/Requirement ........................................................................................... 13

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3.3 Quantity of Water Available............................................................................................ 13

3.3.1 Rainwater Harvesting................................................................................................ 13

3.3.1.1 Rainfall Data ...................................................................................................... 13

3.3.1.2 Catchment Characteristics .................................................................................. 14

3.3.1.3 Quantity of Water for Rainwater Harvesting ..................................................... 14

3.3.2 Borehole Water ......................................................................................................... 15

3.3.2.1 Quantity of Water for Boreholes ........................................................................ 15

3.3.3 Comparison of Water Availability and Reliability ................................................... 15

3.4 Storage Capacity Required .............................................................................................. 15

3.4.1 Storage Capacity for Rainwater Harvesting ............................................................. 15

3.4.2 Storage Capacity for Borehole Water ....................................................................... 15

3.5 Water Quality: Laboratory Tests .................................................................................... 15

CHAPTER FOUR ......................................................................................................................... 17

4.0 RESULTS AND DISCUSSIONS ....................................................................................... 17

4.1 Water Demand/Requirement ........................................................................................... 17

4.3 Quantity of Water Available............................................................................................ 18

4.3.1 Rainwater Harvesting................................................................................................ 18

4.3.1.1 Rainfall Data and Analysis ................................................................................. 18

4.3.1.2 Catchment Characteristics .................................................................................. 20

4.3.1.3 Quantity of Water ............................................................................................... 20

4.3.2 Borehole Water ......................................................................................................... 22

4.3.2.1 Quantity of Water Available .............................................................................. 22

4.3.3: Comparison Of Water Availability and Reliability ................................................. 23

4.4 Storage Capacity Required .............................................................................................. 24

4.4.1 Storage Capacity for Rainwater Harvesting ............................................................. 24

4.4.2 Storage Capacity for Borehole Water ....................................................................... 26

4.4.3 Comparison of the Storage Capacity Required ......................................................... 26

4.5 Water Quality .................................................................................................................. 28

CHAPTER FIVE .......................................................................................................................... 39

5.0 CONCLUSIONS AND RECOMMENDATIONS ............................................................. 39

5.1 Conclusion ....................................................................................................................... 39

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5.2 Recommendations ........................................................................................................... 39

REFERENCES ............................................................................................................................. 41

APPENDICES .............................................................................................................................. 42

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LIST OF FIGURES

Figure 4.5(a): pH Variation........................................................................................................... 29

Figure 4.5(b): Colour Variations................................................................................................... 30

Figure 4.5(c): Conductivity Variations ......................................................................................... 30

Figure 4.5(d): Iron Variations ....................................................................................................... 31

Figure 4.5(e): Turbidity Variation ................................................................................................ 32

Figure 4.5(f): Chlorides Variation ................................................................................................ 32

Figure 4.5(g): Total Hardness Variation ....................................................................................... 33

Figure 4.5(h): Alkalinity Variation ............................................................................................... 34

Figure 4.5(j): Nitrates Variation ................................................................................................... 35

Figure 4.5(k): Total Suspended Solids Variation ......................................................................... 36

Figure 4.5(l): Dissolved Solids Variation ..................................................................................... 36

Figure 4.5(m): Fluorides Variation ............................................................................................... 37

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LIST OF TABLES

Table 2.1.1: Consumption Rates of Water ...................................................................................... 5

Table 2.1.3: Run-Off Coefficients .................................................................................................. 6

Table 4.1: Water Demand for a Household .................................................................................. 17

Table 4.3.1.1 (a): Rainfall Data .................................................................................................... 18

Table 4.3.1.1 (b): Annual Rainfall Data ....................................................................................... 19

Table 4.3.1.1 (c): Monthly Rainfall Data Analysis ....................................................................... 20

Table 4.3.1.3 (a) : Minimum Roof Area Required ....................................................................... 21

Table 4.3.1.3 (b): Run-off for different Roof Area ....................................................................... 22

Table 4.3.2: Borehole Test Yield in Syokimau............................................................................. 23

Table 4.3.3: Quantity of Water Available For an Estate ............................................................... 23

Table 4.4.1(a): Storage Capacity for Low Class Housing ............................................................ 24

Table 4.4.1(b): Storage Capacity for Medium Class Housing ...................................................... 25

Table 4.4.1(c): Storage Capacity for High Class Housing............................................................ 26

Table 4.4.2: Storage Capacity Required For Borehole Water ...................................................... 26

Table 4.4.3: Comparison of Water Storage Capacity Required.................................................... 27

Table 4.5: Water Quality Obtained from Laboratory Results....................................................... 28

Table 4.5(g): Hard/Soft Classification of Water ........................................................................... 33

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CHAPTER ONE

1.0 INTRODUCTION

1.1 Background Information

In places where there is no piped water alternative sources of water have to be obtained. These

alternatives depends on uses and location. Places with a constant and abundant rainfall, water

harvesting systems are adopted as alternative sources. Boreholes are drilled to tap underground

water in places with aquifers or known water tables conditions and levels. In coastal and salty lake

regions, clean water is obtained by removal of salt and other mineral from saline water in a process

known as desalination.

Water harvesting involves capturing the rainwater as it rains, store it in a devised storage facility

and use it later. Borehole involves tapping the ground water to a temporary storage and use it for

daily consumption.

While selecting an alternative source of water, one considers the availability, reliability, and water

quality, safety of the water and cost of the source. Availability and reliability of rainwater

harvesting can be determine by studying the rainfall characteristics of an area while for borehole

water, the geology of an area can explain characteristic of aquifer and groundwater variations.

The quality of water can only be ascertain through laboratory test of several mineral components.

However there are several expectations for different sources. The water in a raindrop is deemed to

be the cleanest source of water available. Absorption of gases such as carbon dioxide, oxygen,

nitrogen dioxide, sulphur dioxide and capture of soot and other microscopic particles may occur

but nevertheless rainwater is still considered as pure before it reaches the ground. Contamination

occurs mostly on the catchment areas. Borehole water has low total suspended solids (TSS),

bacteriological and organic content but has high total dissolved solids (TDS), temporary hardness,

iron, manganese and nitrite contamination. The type of rock which stores the underground water

says a lot about the mineral that could possibly dissolve in borehole water. Safety of water from

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these sources can only be guaranteed after the sampling indicates that the water meet the specified

parameters.

The evaluation of cost is an important parameter when selecting water source. There are two costs

to be considered, the initial cost of establishment and the routinely cost due to operation and

maintenance of the source. Generally, the initial cost of a roof catchment water harvesting system

is lower as the catchment is part of the house. The only extra cost incurred is for the storage facility

and the collection mechanism. Maintenance cost is also minimum which includes cleaning of the

gutters and the storage tank. On the other hand, borehole may require a smaller storage provision

but still the initial cost is very high which may include sinking a borehole 150m below the ground

surface or even lower depth and provision of pumping mechanism. Operation cost includes the

cost of power used for pumping which is on daily basis and routinely the pump system need to be

maintained.

The best alternative source of water is one that ensures water is available and reliable, the quality

and safety can be guaranteed and has the least cost. However one may not achieve all of these

parameter and therefore the source selected is one that will have greater benefits than the other.

In this project, the focus will be on comparison of rainwater harvesting with borehole water as

alternative sources of water in Syokimau, the area of study. This study is important since no official

assessment has been done to assess these alternatives in the area. Evaluation of cost, availability

and reliability of the sources, water quality and its safety will be handy to the communities staying

or planning to stay in Syokimau. This will not only help the future residents but also the current

ones who already rely on one of these sources.

1.2 Problem Statement

Syokimau emerged as a result of urbanization of Nairobi and the need for accommodation. The

area of study is a sub location in Machakos County. It is a residential area located at the south of

Nairobi, the capital city of Kenya. Single dwelling units and residential flats in estates are common

in the area.

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Lack of piped water system is common in the country and therefore affected areas consider

alternative sources of water. For this reason, Kenya is classified as a water stressed country.

Syokimau is no exception to this problem. Currently, there is no piped water in the area and

therefore people are left with two other alternatives sources of water, borehole or rainwater

harvesting. Water use in the area is mostly for domestic purpose including, drinking, cooking,

washing clothes, toilets, bathroom showers and gardening. Without access to water, living in the

area becomes almost impossible. People need water on daily basis. Sanitation is only possible in

presence of water.

The two alternatives will be assessed and report will be provided to help people of Syokimau

choose the better suited source of water.

1.3 Objectives

The overall objective of this project is to compare water harvesting with borehole water as

alternative sources of water in Syokimau. The specific objectives includes the following;

i. Evaluate the quantity of water available for domestic use in Syokimau from water

harvesting and boreholes.

ii. Evaluate the storage capacity required for water harvesting and borehole water for a

household in Syokimau.

iii. Evaluate water quality for water harvesting and borehole water and compare with standards

for drinking water.

iv. Compare water harvesting and borehole water in Syokimau and recommend the better

alternative source of water for domestic use.

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CHAPTER TWO

2.0 LITERATURE REVIEW

2.1 WATER HARVESTING

Water Harvesting is a system that collects rainwater from where it falls rather than allowing it to

drain away. There are various ways of harvesting water. They include; capture run-off from

rooftops, capture run-off from local catchment, capturing seasonal floods water from local streams

and conserving water through watershed system.

In this study, water harvesting is carried out to collect water for domestic use and therefore the

system used to harvest rainwater is capturing run-off from rooftops.

Factors Considered in Water Harvesting

While planning for a water harvesting system for domestic use, one should consider several things.

Among them is the water demand/requirement for a household, rainfall and catchment

characteristics, quantity of water available, storage requirement, the quality of water and safety,

the extent of water uses and the possible sources of pollution and the treatment methods to be

deployed.

2.1.1 Water Requirement/Demand

Water demand depends on uses and the number of water users in the area which may vary from

commercial to domestic water demand. Table 2.1.1 shows consumption rates of water for domestic

water use.

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Table 2.2.1: Consumption Rates of Water

(Design Manual for water supply in Kenya – MOWI, 2005)

Consumer Unit Rural Areas Urban Areas

High

Potential

Medium

Potential

Low

Potential

High

Class

Housing

Medium

Class

Housing

Low

Class

Housing

People with

individual

Connection

Liters/head/day 60 50 40 250 150 75

People without

connection

Liters/head/day 20 15 10 20

Livestock unit Liters/head/day 50 -

The water demand for different cases can be computed from table 2.1.1 provided that there is

sufficient and accurate data available.

2.1.2 Rainfall Characteristics

The prior knowledge of rainfall characteristics, such as the intensity and the distribution over a

period of time, is essential in water harvesting systems. These characteristics helps to establish the

quantity of water available and the storage facility to be provided. The availability of accurate

rainfall data is crucial as it helps not only to get the run-off but also factor in the drought periods

and frequency of rains. Therefore water from the short rains and long rains will be conserved for

use in dry periods.

The Design Manual for water supply in Kenya (MOWI 2005) recommends that the 90%

probability annual rainfall to be used as the dependable rainfall for the purpose of rainwater

harvesting for domestic use.

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2.1.3 Catchment Characteristics

The catchment is the surface where the rain falls to before heading to the collection mechanism.

There are three types of catchment areas depending on the surface:

Type 1 areas: These are the hard surfaces such as roof and rocks. Total run-offs occurs in such

areas.

Type 2 areas: Half run-offs occurs in these areas which are characterized by semi-hard surfaces

such as roads, rocky slopes and compound around a house.

Type 3 areas: These areas are characterized by loose soil surfaces such as fields and valleys and

quarter run-offs may be collected from such areas.

The characteristics of a catchment helps in choosing the run-off coefficients. Table 2.1.3 shows

run-off coefficients for different types of catchment surfaces.

Table 2.1.3: Run-Off Coefficients

(Design Manual for water supply in Kenya – MOWI, 2005)

Surface Type Run-off Coefficient

Roof tiles, corrugated sheets, concreted bitumen, plastic sheets 0.8

Brick pavement 0.6

Compacted soil 0.5

Uncovered surface, flat terrain 0.3

Uncovered surface, slope 0-5% 0.4

Uncovered surface, slope 5-10% 0.5

Uncovered surface, slope >10% >0.5

2.1.4 Quantity of Water Available (Run-off) and Storage Requirement

To get the total run-off of a catchment the following are needed; Total area of the catchment in

square meters (m2), The mean annual rainfall data from the nearest station in the area in

millimeters (mm) and Selection of the run-off coefficient from the characteristic of catchment.

The Total Run-off = Run-off Coefficient x Mean Annual Rainfall x Catchment Area

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Where; Mean Annual Rainfall in m and catchment area is in m2, the total run-off obtained is in m3.

The Design Manual for water supply in Kenya – October 2005, recommends the estimate of

minimum roof area for a roof catchment to be obtained using the following formula;

𝐴 =450𝐷

𝑅

Where:-

A = Minimum roof area in m2

D = Total water demand in liters/day

R = The 90% - probability annual rainfall in mm

To determine the storage facility required, several methods can be adopted including the following;

(a) Balance Method; in this method, the supply of water (yields) is balanced with the user demand

at the end of each month and the storage left in the tank. If the storage at end of each month can

never be less than zero, then this method can be assumed to determine the minimum tank size

required to sustain water use of a family.

The basic formulae (balance equation) is:-

S = S(I) + I - D

Where:-

S = storage at the end of the month

S(I) = the amount stored at the end of previous month

I = product of monthly rainfall x roof area x loss factor

D = amount of water used by a family in a given period.

(b) Cumulative Supply and Demand; this method involves calculation of supply and demand

with the cumulative supply and demand. By using graphical or analytical (calculation) method, the

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maximum difference between supply and demand is determined. The difference is the minimum

size tank.

(c) Dry Season Storage Method; Involves computation of storage requirement for the dry season

only.

Tank size = No. of dry days x daily water use

(d) Collecting all the rainfall and storing; in this method, the total size tank size equals to the

total supply of water in the year.

Tank size = Annual rainfall x roof area x 90%

2.1.5 Quality of Water and its Uses

Rainfall water is very pure and has a very good quality for domestic uses. However the catchment

condition adversely affects its quality as it changes the quality and causes several contaminations.

Type 1 areas (Hard Surfaces, Roof and Rocks) has potential of harnessing clean water for human

consumption. Type 2 areas (Semi-hard surfaces such as roads, house compound and rocky valley)

has a potential of proving fairly clean water for livestock, gardening, fish farming and biogas

generation among others. The Type 3 areas (loose surfaces) may provide water for irrigation,

construction of holding dams, shallow wells and ponds.

In our case study, roof water harvesting is adopted and therefore the quality of water is

substantially good and can be used for human consumption with minimum treatment.

Several tests are conducted to ascertain that the water harvested meet the required standards which

will be discussed in details later.

2.1.6 Sources of Pollution and Treatments of Rainwater Harvesting

The quality of rainwater deteriorates mainly during harvesting, storage and household use. The

sources of contamination includes, wind-blown dirt, leaves, fecal dropping from birds and animals,

insects and contaminated litter on the catchment areas. Poor hygiene in storing water or at the point

of use also presents a major health concern.

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The above risks and hazards can however be minimized by a good design and practice. Provision

of first-flushing systems ensures the dust and other particles that settled on the roof is cleaned

away and does not find its way to the storage tank. A small sedimentation tank at the entry of

storage may help to settles finer particles while a filter mechanism at the entry point trap leaves

and other larger objects. Constant cleaning of the gutters to remove leaves and other trapped

objects such as bird nest before the rainy season is a good practice to maintain a cleaner system.

Use of disinfectant before using the water for drinking is highly recommended so as to kill the

bacteria.

2.2 BOREHOLE WATER

Underground water is used as sources of water in many areas where supply of water does not meet

the demand or not established. The underground water is obtained by drilling of boreholes when

in deep depth, hand dug wells in places with shallow water tables or springs in places where the

geology allows its occurrence.

The main source of ground water is precipitation. The rainwater infiltrate the ground and percolates

through channel to the ground water. However not all water that infiltrate the soil becomes

groundwater. Some of the water may be pulled back to the surface by capillary forces and hence

evaporates. It may also be absorbed by plants root and find its way to the atmosphere through the

process of transpiration.

Underground water occurs in aquifers. An aquifer is a water bearing stratum/geological formation

that stores and transmit water through its pores at relatively large rates. Aquifer stores enough

water for economical extraction of water by wells. They are usually made of coarse materials such

as gravels and sand so as to achieve higher porosity for storage and transmission of water.

The aquifers are of two types. Unconfined aquifer is one that extends from the ground surface to

the impervious stratum underneath while a confined aquifer is one that is sandwiched between two

impervious stratums.

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2.2.1 Extraction and Quantity of Water in Boreholes

Extraction of groundwater is primarily done through construction of boreholes or infiltration

galleries. A borehole used as a water well is typically made of three elements; the well structure,

the pump and the discharge pumping. The well structure consists of perforated casing or slotted

metal screen through which water enters to the well.

Several factors are considered in determining the quantity of water to be obtained from a borehole.

In some cases, relatively simple mathematical expressions are utilized while in other cases the

estimations can only be done using graphical analysis or the use of various kinds of models.

Water in a confined aquifer is under pressure and are known as artesian aquifers. A well

penetrating though an artesian aquifer will have water rising to the local static pressure (artesian

head). If the artesian head is above the ground surface, water will flow freely to the ground surface

and therefore a flowing artesian well will be formed. A non-flowing artesian well is one that the

artesian head is below the ground surface and therefore pumping is required to get the water to the

surface.

When water is pumped from a well, the water table in the well and its vicinity will be lowered and

this is referred as ‘drawdown’. This causes the artesian pressure surface to develop a circular

depression called a cone of depression.

The yield of a water borehole is in most cases obtained after the construction of the well is

completed and the pumping tests are done.

2.2.2 Storage Requirement for a Water Borehole

A fully functioning water borehole with known yield guarantees water supply and therefore the

storage capacity can be minimized to a daily storage requirement. This storage can be estimated

by utilization of balanced method or cumulative demand and supply curve. A bigger storage may

be used to act as a buffer in the case of pump failure or power outages.

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2.2.3 Borehole Water Quality

Underground water are stored in aquifers. The aquifer rocks constitutes several mineral

compounds some of which can be dissolved. Water is known as the universal solvent because it

dissolves more substances than any other solvent. Therefore minerals in the rocks are dissolved

when they come to contact with water. The most common dissolved mineral substances are

sodium, calcium, magnesium, potassium, chlorides, bicarbonates and sulphates. These minerals

are known as common constituents in water chemistry.

Minerals dissolved in underground water gives it a tangy taste which is enjoyable by people while

drinking it. Without the dissolved minerals, water have a flat taste which is not very appealing to

humans. However if these mineral are in excess, it becomes undesirable to use the water for

drinking. The limit for dissolved mineral is 1000 mg/L (Guidelines for Drinking-water Quality –

WHO, 2011).

When dissolved mineral are in large concentration, water becomes hazardous to both animals and

plants. For instance, high concentration of sodium is harmful to people with heart problem while

high concentration of boron is toxic to some plants. Water that contains a lot of calcium and

magnesium is said to be hard. Very hard water is not desirable for many domestic uses as it leave

a scaly deposit on pipes, water heaters and water tanks while extremely soft water is likely to

corrode metals. Minerals also have adverse effect on alkalinity, pH and conductivity of the water.

2.2.4 Pollution Sources and Treatment of Borehole Water

The growth of industry, technology, population contributes a lot to underground water pollution.

Domestic and industrial wastes, chemical fertilizers, herbicides and pesticides are not properly

contained and have entered the soil, infiltrated some aquifers and degrades the quality of

underground water. Other pollution sources includes sewer leakage, faulty septic tanks and landfill

leachates.

Groundwater is less susceptible to bacterial pollution than surface water. This is mostly because

of the soil and rocks that transmit the water screens out most of the bacteria. However, bacterial

contamination may occur when storage facilities and point of use is of poor hygiene.

http://chemistry.about.com/od/waterchemistry/f/Why-Is-Water-The-Universal-Solvent.htm

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The treatment of the borehole water depends on the quality evaluation made. Hard water can be

softened at a fairly reasonable cost. Minimum disinfection can be done to ensure bacterial

contamination is eliminated. It is however expensive to remove all the dissolved minerals and

therefore undesirable. In case of toxic contamination, it is much safer and inexpensive to abandon

the use of borehole water than treated it.

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CHAPTER THREE

3.0 METHODOLOGY

3.1 Introduction

This Chapter describes methods and technique that were used in collection of data, analysis and

experimentations which helps in accomplishing the project’s objective, that is, comparison

between water harvesting and borehole water as alternative sources of water in Syokimau.

3.2 Water Demand/Requirement

The study area is identified as a residential area and therefore the water demand was estimated for

domestic consumption. Daily, Monthly and annual water demand for high class and middle class

housing were obtained in accordance to the design manual for water supply in Kenya – October

2005.

3.3 Quantity of Water Available

3.3.1 Rainwater Harvesting

3.3.1.1 Rainfall Data

The nearest weather station was identified as J.K.I.A meteorological station. Monthly rainfall data

for the station were obtained from the Kenya Meteorological Department for 23 years. Using the

mean arithmetic method, the average annual rainfall was obtained from the data. The 90%

probability annual rainfall in mm was also computed using the normal distribution. The following

formulas were adopted;

Arithmetic Mean;

�̅� =1

𝑁∑ 𝑋𝑖𝑁𝑖=1

The Sample Standard Deviation;

𝑆 = √1

𝑁−1∑ (𝑋𝑖 − �̅�)2𝑁𝑖=1

Probability Using the Normal Distribution Table;

𝑍 =𝑋𝑖−�̅�

𝑠

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Where; �̅� is the mean

𝑋𝑖 is Data values

S – is the Sample Standard Deviation

Z = is the Z – Score (Normal Distribution Table)

N- Number of the samples

3.3.1.2 Catchment Characteristics

The water harvesting system to be used in the area was identified as use of house roof as catchment.

Using the Design Manual for water supply in Kenya – October 2005, the run-off coefficient was

selected to fit the catchment.

3.3.1.3 Quantity of Water for Rainwater Harvesting

Using the rainfall data and the water demand computed before, different catchment areas were

estimated for middle class and low class housing using the formula;

𝐴 =450𝐷

𝑅

Where:-




Several catchment areas in square meters were selected as representation of different possible roof

areas for different types of houses. The total run-off was the obtained as follows;



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3.3.2 Borehole Water

3.3.2.1 Quantity of Water for Boreholes

Data of Yield Test were obtained from WRMA databases for groundwater of the study area. The

arithmetic mean of the water yield was obtained for the data. The mean yield was then used as the

quantity of water for the boreholes in the area.

3.3.3 Comparison of Water Availability and Reliability

A comparison of quantity of water available for an estate consisting of 40 medium class housing

will be made for both water harvesting and borehole water.

3.4 Storage Capacity Required

3.4.1 Storage Capacity for Rainwater Harvesting

The method of cumulative supply and demand was used to determine the minimum size tank

required. The demand for a single household was used and the average monthly water rainfall was

used to determine supply. Using analytical method, the size tank was determined. This was done

by getting the cumulative deficit and surplus for different months. The maximum difference

between cumulative supply and demand obtained was the optimum tank size.

3.4.2 Storage Capacity for Borehole Water

The storage required was the daily requirement for different types of house classes and multiplied

by a factor of 3.0 to account for power outages and mechanical failures of pumping equipment.

The factor will provide a buffer storage that will ensure supply of water continues in the case of

power blackout and mechanical failure or maintenance of the pumping equipment.

3.5 Water Quality: Laboratory Tests

Water samples for borehole water and water harvesting were obtained from the study area. A single

sample for each alternative water source was taken as representation of the area of study.

Permission for taking the samples from the household owner were obtained. The samples was

taken by first rinsing the sampling bottle three times and the taking a liter of water for each sample.

The same was done using a 100ml sterilized bottles for taking samples for bacteriological

examination.

16 | P a g e

Laboratory tests were carried out for each of the sample obtained in accordance to the Standard

Methods for the Examination of Water and Wastewater (APHA, 2005). The tests to be carried

were selected in accordance to the availability of chemical reagents and equipment in the Public

Health Laboratory. Tests to obtain the following parameters were carried out;

a) pH

b) Colour

c) Conductivity

d) Iron

e) Turbidity

f) Chlorides

g) Total Hardness

h) Alkalinity

i) Dissolved Oxygen

j) Nitrates

k) Total Suspended Solids

l) Dissolved Solids

m) Fluorides

n) Bacteriological Examination

The results obtained were therefore compared to the drinking water standards of World Health

Organization (2011) and the Design Manual for Water Supply in Kenya (2005)

17 | P a g e

CHAPTER FOUR

4.0 RESULTS AND DISCUSSIONS

4.1 Water Demand/Requirement

Syokimau is mostly consisting of modern family residents and therefore assumes that a single

household consists of 6 members, a father, mother, 3 children and a house help/Guest. Water

demand per household is therefore based on 6 members. The following are the water requirement

for different housing classes as per the Design Manual for Water Supply in Kenya (MOWI 2005)

in urban areas;

The water consumption rate obtained in table 4.1 is used to compute the water demand in

Syokimau and helps to determine the storage capacity required while also evaluate water

availability from the sources as whether it meet the water demands in the area.

Table 4.1: Water Demand for a Household

Consumption Unit High Class

Housing

Medium Class

Housing

Low Class

Housing

Individual

Household

member

Liters/ Day/

Person

250 150 75

Household of 6

members

Liters/Day 1500 900 450

Monthly

Consumption

per household

M3/Month 45 27 13.5

Yearly

Consumption

per household

M3/Year 540 324 162

18 | P a g e

4.3 Quantity of Water Available

The results obtained are analyzed below to establish water availability for water harvesting and

borehole and comparison of the two alternative sources of water is made.

4.3.1 Rainwater Harvesting

4.3.1.1 Rainfall Data and Analysis

The following rainfall data for the nearest meteorological station to Syokimau were obtained and

analyzed as follows to establish the total run-off and area of roof that caters for different water

demands in the area.

Table 4.3.1.1(a): Rainfall Data

(Source: JKIA Meteorological Station, Station ID: 9136168, Kenya Meteorological Department)

YEAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

1990 27.1 40.9 179.1 167 556 3.2 5.3 56 17.6 0 173 94.9

1991 9.6 0 98.5 0 209.3 15.6 1.8 6.9 2.4 35.2 841 95.9

1992 3.4 10.2 9.1 228.3 155 12.7 35.7 9.7 0.4 37.7 86.4 132.6

1993 210.9 51.7 17 8.3 51.4 43.2 0 4.1 0 69.7 68.6 83.2

1994 0.6 97.2 48.6 163 58 35.7 3.1 23.7 0 73.1 203 28.1

1995 59.1 79.4 133.3 70.7 86.5 46.9 18.1 17.5 32.3 45.6 29.5 32.4

1996 36.9 69.4 55.8 61.2 55.8 58.5 16.3 12.1 2 0 129 10.6

1997 0 0 35.2 235.6 163.2 6.6 14.7 0 0 308 308 124.9

1998 322.6 125 74.2 110.4 322.5 69.9 31.3 6.2 18.9 0 74.2 6.4

1999 0 1.3 123.5 91.6 3 1.9 3.9 32.9 0 37.9 251 95.9

2000 13.4 0 18.5 74.8 18.7 26.9 1 1.4 8 11.6 113 37.4

2001 306.5 10.7 161.3 67.2 38.3 13.7 19.9 14.3 3.7 33.6 199 15.9

2002 57.6 15.1 99.1 151.9 158.9 0.8 0.2 3.9 54.5 48.7 115 331.2

2003 16.9 9.5 22.1 154.6 229.8 6.8 1.6 47.8 40.8 52.3 120 25.2

2004 33.7 76.2 93.3 137.6 57.9 2.9 0 0.6 26.5 65.3 125 0.4

2005 36.7 1.4 46.3 130.2 89.5 3.7 11.7 0.3 9.1 6.6 65.5 1.2

2006 5.2 38 124.5 222.9 98.2 0.2 0 27.8 5.5 0 233 19.2

2007 83.4 18.2 35.8 195.7 52.8 27.2 18 12 19.6 23.7 95 0

2008 51.3 24.1 193.2 81 4.7 1.5 27.2 3.2 35.4 101 82.6 0

2009 52.4 34.1 27.1 84.5 140 36.6 5 0.6 2.3 65.6 48.6 112.7

2010 68.9 96.7 132.1 54 81.1 26.6 1.3 6.6 13.9 34.9 77.5 55.7

2011 1.8 74.8 92.7 17.8 44.5 29.6 2.9 42.2 27.8 46.9 250 29.1

2012 0 2.4 5.2 288.8 199.6 32.2 13.4 3.8 36.3 63.7 64.8 259.1

19 | P a g e

Table 4.3.1.1(b): Annual Rainfall Data

YEAR Annual Rainfall (mm)

1990 1320.0

1991 1316.0

1992 721.2

1993 608.1

1994 734.1

1995 651.3

1996 507.6

1997 1196

1998 1162

1999 643

2000 325.1

2001 883.7

2002 1037

2003 727.2

2004 619.2

2005 402.2

2006 774.5

2007 581.4

2008 605.2

2009 609.5

2010 649.3

2011 659.7

2012 969.3

The Annual Mean Rainfall = 769.7 mm

The Sample Standard Deviation = 274.8 mm

From the normal distribution table Z=1.28 for P(x) = 0.9

The 90% Probability Annual Rainfall = 1121.4 mm

The annual rainfall analyzed above established that the 90% probability annual rainfall is

1121.44mm of rainfall which is recommended in computation of the minimum roof area and the

total run-off for a roofing system.

The monthly rainfall data are analyzed in table 4.3.1.1 (c) so as to get the 80% probability

monthly rainfall which helps to obtain the most economical and sufficient storage capacity.

20 | P a g e

Table 4.3.1.1(c): Monthly Rainfall Data Analysis

Month JAN FEB MAR APR MAY JUN JUL AUG SEPT OCT NOV DEC

Average

Rainfall (mm)

60.8

38.1 79.4 121.6 125.0 21.9 10.1 14.5 15.5 52.8 163.1 69.2

Standard

Deviation

92.1 38.2 56.8 77.6 123.7 20.0 10.8 16.3 16.0 62.9 165.7 84.1

80%

Probability

Rainfall (mm)

138.1 70.2 127.1 186.8 228.9 38.7 19.2 28.2 29.0 105.6 302.3 139.8

For P(x) =0.8 Z= 0.84 (Normal Distribution Table)

4.3.1.2 Catchment Characteristics

The method of water harvesting adopted is capturing run-off from rooftop. The surface is therefore

solid and hard as the roofs are mostly corrugated iron sheets or roof tiles (clay). From Design

Manual for Water Supply in Kenya (MOWI 2005), the run-off coefficient to be used is 0.8.

4.3.1.3 Quantity of Water

The roof area required for different water demand can be obtained as follows;

𝐴 =450𝐷

𝑅

Where:-




The roof sizes obtained above are the minimum sizes of roof that can meet the water demand of

different class of households as shown in table 4.3.1.3(a). While planning to use water harvesting

system as alternative source of water in Syokimau, one needs to ensure that the roof size of the

house is greater than the minimum roof sizes in table 4.3.1.3(a).

21 | P a g e

Table 4.3.1.3(a) : Minimum Roof Area Required

Unit High Class

Housing

Medium Class

Housing

Low Class

Housing

Demand Liters/Day 1500 900 450

90% Probability

Rainfall

mm 1121.4 1121.4 1121.4

Minimum Roof

Area

M2 602 361 181

Total Run-off for selected range of roof sizes;



The Run-off Coefficient for a roof is 0.8 while the 90% probability annual rainfall is 1121.4 mm.

Table 4.3.1.3(b) shows the values of total run-off one expects in Syokimau for a certain range of

roof area. The roof sizes in most houses are fixed and therefore one can estimate the amount of

water available from water harvesting from the roof area. A large roof area provides a bigger water

collection surface and hence higher total run-off is anticipated.

22 | P a g e

Table 4.3.1.3(b): Run-off for different Roof Area

Roof Area (m2) Total Run-off (m3)

125 112.1

150 134.6

175 157.0

200 179.4

225 201.9

250 224.3

275 246.7

300 269.1

325 291.6

350 314.0

375 336.42

400 358.9

425 381.3

450 403.7

475 426.1

500 448.6

4.3.2 Borehole Water

4.3.2.1 Quantity of Water Available

The following data were obtained from WRMA underground water department for the boreholes

in Syokimau;

From the test yield data obtained, the average yield one can expect in Syokimau is 160.9

liters/minute. The water yield can vary depending on the time of the year and the number of new

boreholes in the vicinity, the yearly changes in the annual rainfall and the local detrimental effects

of increased transpiration as a result of the planting of large numbers of trees. The average test

yield obtained above indicates that there is plenty of underground water for a single household

however it is important that one do not pump more than what they need as underground water is a

very precious resource and should not be wasted.

23 | P a g e

Table 4.3.2.1: Borehole Test Yield in Syokimau

(Source: Water Resource Management Authority – Nairobi Regional Office)

Owner Permit No. Total

Depth

(m)

Struck

(m)

Rest

(m)

Test

Yield

lpm

George Kinyua WRMA/ACB/702 200 116 96. 176.7

Wachuka Waruigi WRMA/ACB/526 175 114 96 200

Andrew Wanyoike WRMA/ACB/6905/8 182 128 - 100

All Pack Industries WRMA/ACB/669 154 146 107 167

4.3.3: Comparison of Water Availability and Reliability

For an estate consisting of 40 medium class housing, the quantity of water available from water

harvesting and borehole water can be estimate as shown in table 4.3.3

Table 4.3.3: Quantity of Water Available For an Estate

Water Harvesting

Roof Area per household (m2) 361

Water Harvested Per household (m3) 324

Roof Area for Estate (m3) 14440

Water Harvested For Estate (m3) 12960

Borehole

Yield rate (lpm) 160.9

Demand for the estate per year (m3) 13140

Pumping time per day (Hours) 4

Yearly Yield (m3) 14095

The analysis in table 4.3.3 indicates that both alternative sources of water can yield enough water

for domestic use in Syokimau if and only if a proper design is established. However borehole water

is available in plenty and its yearly and seasonal variation will not affect the yield substantially to

cause water stress for a household. Variation in rainfall is unpredictable and can largely affect the

amount of water available to support demand of a household. Drought periods will make it

impossible for the households in Syokimau to rely on water harvesting system. Therefore the

24 | P a g e

quantity of water available in boreholes is much higher than that of water harvesting and can be

greatly relied upon.

4.4 Storage Capacity Required

4.4.1 Storage Capacity for Rainwater Harvesting

The storage capacity can be obtained as follows;

(a) Low Class Housing

The storage capacity required for low class housing is obtained from table 4.4.1(a) as 48800 liters.

This is the most economical storage capacity which can meet the demand of a household for

domestic use of water in Syokimau for a low class housing system.

Monthly Water Demand - 13500 l

Minimum Roof Area - 181 m2

Table 4.4.1(a): Storage Capacity for Low Class Housing

Month

80%Prob.

Rainfall

(mm)

Supply S

(l)

Demand D

(l)

Surplus

(l)

Deficit

(l)

Cum.

Surplus

(l)

Cum.

Deficit

(l)

Jan 138.1 22496.5 13500 8996.5

Feb 70.2 11435.6 13500 2064.4

Mar 127.1 20704.6 13500 7204.6

Apr 186.8 30429.7 13500 16929.7 47922.1

May 228.9 37287.8 13500 23787.8

Jun 38.7 6304.2 13500 7195.8

Jul 19.2 3127.7 13500 10372.3

Aug 28.2 4593.8 13500 8906.2 35250.21

Sept 29.0 4724.1 13500 8775.9

Oct 105.6 17202.2 13500 3702.2

Nov 302.3 49244.7 13500 35744.7 48720.3

Dec 139.8 22773.4 13500 9273.4

25 | P a g e

(b) Medium Class Housing

Table 4.4.1(b) shows that the storage capacity required is 96950 liters. This is the minimum storage

and most economical storage tank required for one to use water harvesting as alternative source of

water in Syokimau for a middle class housing system.



Table 4.4.1(b): Storage Capacity for Medium Class Housing

Month

80%Prob.

Rainfall

(mm)

Supply S

(l)

Demand

D (l)

Surplus

(l)

Deficit

(l)

Cum.

Surplus

(l)

Cum.

Deficit

(l)

Jan 138.1 44868.7 27000 17868.7

Feb 70.2 22808.0 27000 4192.0

Mar 127.1 41294.8 27000 14294.8

Apr 186.8 60691.3 27000 33691.3 95355.7

May 228.9 74369.6 27000 47369.6

Jun 38.7 12573.6 27000 14426.4

Jul 19.2 6238.1 27000 20761.9

Aug 28.2 9162.2 27000 17837.8 70604.01

Sept 29.0 9422.1 27000 17577.9

Oct 105.6 34309.4 27000 7309.4

Nov 302.3 98217.3 27000 71217.3 96947.7

Dec 139.8 45421.0 27000 18421.0

(c) High Class Housing

From table 4.4.1(c) the Storage Capacity required is obtained as 161800 liters. The economical

storage capacity required to sustain a high class housing in Syokimau is too large and may be

impractical as it will be very expensive to construct and occupy a large space.



26 | P a g e

Table 4.4.1(c): Storage Capacity for High Class Housing

Month

80%Prob.

Rainfall

(mm)

Supply S

(l)

Demand D

(l)

Surplus

(l)

Deficit

(l)

Cum.

Surplus

(l)

Cum.

Deficit

(l)

Jan 138.1 74822.6 45000 29822.6

Feb 70.2 38034.4 45000 6965.6

Mar 127.1 68862.8 45000 23862.8

Apr 186.8 101208.2 45000 56208.2 159089.0

May 228.9 124018.0 45000 79018.0

Jun 38.7 20967.7 45000 24032.3

Jul 19.2 10402.6 45000 34597.4

Aug 28.2 15278.8 45000 29721.2 117638.8

Sept 29.0 15712.2 45000 29287.8

Oct 105.6 57214.1 45000 12214.1

Nov 302.3 163786.1 45000 118786.1 161743.9

Dec 139.8 75743.6 45000 30743.6

4.4.2 Storage Capacity for Borehole Water

The following are the storages for different housing classes;

Storage = Daily Demand x 3.0

Table 4.4.2: Storage Capacity Required For Borehole Water

Housing Class Demand liters/day Storage (Liters)

High 1500 4500

Medium 900 2700

Low 450 1350

The factor of 3.0 used above is to account for power outages which are common in the country

and may go on for days. It also accounts for mechanical errors and maintenance of the pumping

mechanism of the borehole.

4.4.3 Comparison of the Storage Capacity Required

The storage capacity required for water harvesting system in Syokimau is found out to be very

large compared to that of borehole water. The comparison can be shown in table 4.4.3 for a

household of 6 family members

27 | P a g e

Table 4.4.3: Comparison of Water Storage Capacity Required

Housing Class Water Storage Capacity (Liters)

Water Harvesting Borehole Water

High 48720 4500

Medium 96948 2700

Low 161744 1350

Large storage capacity are very costly and also occupies large spaces. Therefore the storage

capacity of borehole water is less costly and takes smaller space of the house plot.

28 | P a g e

4.5 Water Quality

The following water qualities for the samples collected in Syokimau randomly representing the

area were obtained from the laboratory tests carried out.

Table 4.5: Water Quality Obtained from Laboratory Results

PARAMETERS UNITS RESULTS WHO

STANDARDS

KEBS

STANDARDS WATER

HARVESTING

BOREHOLE

WATER

pH pH Scale 7.13 8.4 6.5-8.5 6.5-8.5

Colour TCU 5 5 Max 15 Max 15

Conductivity μS/cm 56 586 Max 2500 Max 2500

Iron mg/l 0.2 0.2 Max 0.3 Max 0.3

Turbidity NTU 2.5 0.6 Max 5 Max 5

Chloride mg/l 24 118 Max 250 Max 250

Total Hardness mg CaCO3/l 34 32 Max 500 Max 500

Alkalinity mg CaCO3/l 36 237 Max 500 Max 500

Dissolved Oxygen mg/l 7.85 8.41 - -

Nitrate mg/l 0.5 0 Max 10 Max 10

Total Suspended

Solids

mg/l 20 0 Max 1500 Max 1500

Dissolved Solids mg/l 30 540 Max 1500 Max 1500

Fluoride mg/l 0.35 1.72 Max 1.5 Max 1.5

Coliform Colonies/ml 23 Nil 100 100

The quality of water for water harvesting mainly depends on the surface at which the rainwater

falls to before collection. Rainfall drops are mainly pure water with very less mineral contents.

Borehole water is expected to have higher mineral contents. This is as a result of water dissolved

minerals from the aquifer rocks. The tested parameter for each of the sources can therefore be

analyzed and discussed as follows;

29 | P a g e

a) pH

The pH value obtained for water harvesting sample was 7.13 while that of borehole was 8.4. Both

of the samples are within the acceptable range of values of 6.5-8.5. As expected, rainwater is less

alkaline than ground water. This is mainly attributed to the type of rock and its mineral content

which dissolves in water to form hydroxides which leads to increase in pH. Excessive acidity and

alkalinity is harmful to human health, changes the taste of the water and may cause damage or

blockage of the conduits.

b) Colour

The colour of the samples from both sources, water harvesting and borehole water are 5 TCU. The

maximum allowable colour is 15TCU and therefore the samples were both within the acceptable

range. Colour of water is very important as it makes it appealing for consumers. Water may be

safe for drinking however excess colour may make it less appeal to consumers and therefore may

be avoided.

Figure 4.5(a): pH Variation

6.5

8.5

7.13

8.4

0123456789

Min.

Allowable

Max.

Allowable

Water

Harvesting

Borehole

Water

pH

Val

ue

Alternative Water Source

pH

30 | P a g e

c) Conductivity

The maximum acceptable conductivity of water is 2500μS/cm. The conductivity of the water

harvesting sample was 56μS/cm while that of borehole water was 586μS/cm and hence both

samples were within the acceptable range. Conductivity is the ability of water to transmit electric

or heat which is mainly the ionic activity within the water. Conductivity can therefore be directly

associated with the number of ions in a solution and hence it is higher in water with more total

dissolved solids.

15

5 5

0

2

4

6

8

10

12

14

16

Max. Allowable Water Harvesting Borehole Water

Colo

ur

(TC

U)


Colour

Figure 4.5(b): Colour Variations

2500

56 5860

500

1000

1500

2000

2500

3000


Conduct

ivit

y (

μS

/cm

)


Conductivity

Figure 4.5(c): Conductivity Variations

31 | P a g e

d) Iron

The iron content in both water harvesting and borehole water samples was found to be 0.2mg/l.

The acceptable content of iron in drinking water is 0.3mg/l. Both samples are therefore within the

acceptable range. Iron does not present any health problem in human. It is actually needed to

facilitate oxygen transportation in blood. Iron only present concern when bacteria gets to the water,

since some pathogenic organisms requires iron to grow. It may also leave stains in laundry, utensils

and plumbing fixtures.

e) Turbidity

The turbidity of the water harvesting was found to be 2.5 NTU while borehole water had less

turbidity of 0.6 NTU. This is below the maximum allowable limit of 5 NTU and thus acceptable

for domestic use. Excessive turbidity, or cloudiness in drinking water is aesthetically unappealing

and may also represent health concern. Turbidity can provide food and shelter for pathogens and

hence encourage its growth and reproduction therefore leading to waterborne disease outbreak.

0.3

0.2 0.2

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35


Iron (

mg/l

)


Iron

Figure 4.5(d): Iron Variations

32 | P a g e

f) Chloride

The borehole water sample had higher chloride content of 118mg/l while that of water harvesting

had chloride content of 24mg/l. Due to dissolved content of mineral rocks, ground water as

expected has higher chloride content compared to rainwater. The maximum acceptable limit of

chloride content is 250mg/l and therefore both sample are within the acceptable range. Amount of

chloride in drinking water has less health concern. However if chloride content is higher than the

acceptable amount, water may have a salty taste.

5

2.5

0.60

1

2

3

4

5

6


Turb

idit

y (

NT

U)


Turbidity

Figure 4.5(e): Turbidity Variation

250

24

118

0

50

100

150

200

250

300


Chlo

ride

(mg/l

)


Chlorides

Figure 4.5(f): Chlorides Variation

33 | P a g e

g) Total Hardness

The total hardness for the water harvesting and borehole water samples were 34 mg CaCO3/l and

32 mg CaCO3/l respectively. The maximum allowable hardness is 500 mg CaCO3/l and therefore

both of the sources had water hardness within the acceptable limit.

Table 4.5(g): Hard/Soft Classification of Water

Classification Hardness in mg CaCO3/l

Soft 0 - 60

Moderately Hard 61 - 120

Hard 121 - 180

Very Hard >181

Both water harvesting and borehole water sample can be classified as soft water as they have a

hardness which is less than 60mg/L and therefore good for domestic use. Water hardness has less

health concern. However, hard water may cause soap to precipitate instead of forming lather. It

may also leave scales on water fixtures and hence reduces the pipe size and in severe case may

cause blockage.

250

34 320

50

100

150

200

250

300


Tota

l H

ardnes

s (m

g/l

)


Total Hardness

Figure 4.5(g): Total Hardness Variation

34 | P a g e

h) Alkalinity

The total alkalinity for the water harvesting and borehole water samples were 36 mg CaCO3/l and

237 mg CaCO3/l respectively. The samples are therefore within the acceptable alkalinity of 500

mg CaCO3/l. The alkalinity is the amount of Calcium Carbonate which dissolved in water.

Borehole water has higher alkalinity content as a result of dissolved Calcium Carbonate from

limestone rocks or any other rock with Calcium Carbonate content. Higher alkalinity beyond the

maximum allowable gives water a ‘soda’ taste and may also causes dry of skin.

i) Dissolved Oxygen

The dissolved oxygen of the water harvesting was 7.85mg/l while that of borehole water was

8.41mg/l. A high Dissolved Oxygen level is good as it makes drinking water taste better, however

water with very high dissolved oxygen may cause corrosion of water pipes.

500

36

237

0

100

200

300

400

500

600


Alk

alin

ity

(mg/l

)


Alkalinity

Figure 4.5(h): Alkalinity Variation

35 | P a g e

j) Nitrates

The borehole water sample had no nitrate content while the nitrate content of water harvesting

sample was 0.5mg/l. The maximum allowable limit of nitrate is 10mg/l. Both samples are therefore

within the acceptable limit. Infants below six months who drink water containing nitrate in excess

of the maximum contaminant level could become seriously ill and, if untreated, may die.

Symptoms include shortness of breath and blue baby syndrome. Nitrate contamination in rainwater

may be as a result of bird and animal poops on the collecting surface while fertilizers are mainly

responsible for nitrate contamination of ground water.

k) Total Suspended Solids

The borehole water sample had no suspended solids while the total suspended solids of water

harvesting sample was found to be 20 mg/l. Both samples are within the acceptable limit of

1500mg/l. Suspended solids consist of an inorganic fraction (silts, clays) and an organic fraction

(algae, zooplankton, bacteria, and detritus). For rainwater harvesting, suspended solids comes from

the collecting surface while in boreholes, suspended solids get into water from the aquifer when

the strainer is ineffective or failed. Total suspended solids may present health concern in rare cases

but mainly it may cause cloudiness that may contribute to turbidity and therefore interfere with

aesthetics of water.

10

0.5 00

2

4

6

8

10

12


Nit

rate

s (m

g/l

)


Nitrates

Figure 4.5(j): Nitrates Variation

36 | P a g e

l) Total Dissolved Solids

As a result of dissolved mineral from the aquifer rocks in underground water, the dissolved solids

for borehole water sample was found to be 540mg/l which is higher compared to that of water

harvesting sample, 30mg/l. For both samples, the total dissolved solids are below the maximum

acceptable value of 1500mg/l and therefore making the water suitable for consumer use and

domestic use.

1500

20 00

200

400

600

800

1000

1200

1400

1600

Max. Allowable Water Harvesting Borehole WaterTo

tal

Susp

ended

Soli

ds

(mg/l

)


Total Suspended Solids

Figure 4.5(k): Total Suspended Solids Variation

1500

30

540

0

200

400

600

800

1000

1200

1400

1600


Dis

solv

ed S

oli

ds

(mg/l

)


Dissolved Solids

Figure 4.5(l): Dissolved Solids Variation

37 | P a g e

m) Fluorides

Fluoride content of ground water is higher compared to rain water. This is a result of presence of

fluoride in aquifer rocks which dissolve in when comes into contact with underground water. The

borehole water sample was found to have fluoride content of 1.72mg/l while the sample of water

harvesting had fluoride content of 0.35mg/l. The maximum allowable fluoride in drinking water

is 1.5mg/l. Borehole water has slightly higher content of fluoride than the acceptable value,

however in many country with geology which has higher content of fluoride places a secondary

acceptable content of 2.0mg/l of fluoride. Considering the secondary limit, the borehole water

sample may have negligible health risk. Exposure to excessive consumption of fluoride over a

lifetime may lead to increased likelihood of bone fractures in adults, and may result in effects on

bone leading to pain and tenderness. Children aged 8 years and younger exposed to excessive

amounts of fluoride have an increased chance of developing pits in the tooth enamel, along with a

range of cosmetic effects to teeth.

1.5

0.35

1.72

0

0.5

1

1.5

2


Flu

ori

de

(mg/l

)


Fluorides

Figure 4.5(m): Fluorides Variation

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n) Coliforms

There was no Escherichia coli bacteria present in the borehole water sample. The water harvesting

sample was found to have presence of Escherichia Coli bacteria of 23 colonies/ml. The acceptable

limit of total viable counts at 37oC is 100 per ml. The rainwater is therefore within the acceptable

range however disinfection is highly recommended when using this water for drinking. This may

include boiling of the water before using for drinking. Presence of coliform bacteria in drinking

water indicates risk of contracting a water-borne disease. Total coliform may come from sources

other than fecal matter however it should be considered as an indication of pollution especially for

positive E.coli results.

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CHAPTER FIVE

5.0 CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusion

This study compared water harvesting and borehole water as alternative sources of water for

Syokomau area. The conclusions of the study were the following;

1. Water availability in Syokimau was higher for boreholes than for water harvesting. For an

estate of 40 medium class households, borehole has an annual yield of 14095m3 of water

for a pumping time of 4 hours per day while water harvesting yields 12960m3 of water.

2. The borehole water is more reliable than water harvesting in the area. This is mainly due

to low rainfall or no rain at all during dry spell.

3. Water harvesting system requires very large storage facility of up to 96950 liters compared

to 2700 liters for borehole water for a middle class household.

4. Water from both alternative sources of water in Syokimau, water harvesting and borehole

water, meet the required quality standards of water in Kenya.

From the above conclusions, it is clear that the borehole water is a better alternative source of

water in Syokimau area compared to rainwater harvesting.

5.2 Recommendations

The recommendation are as follows

1. When planning for water harvesting as alternative source of water, drought season should

be taken into account by ensuring that water can be obtained by means of transport from

any other nearby source.

2. Good design and practice should be adopted for water harvesting so as to ensure that the

risk and hazards of water contamination are minimized include a first-flushing system to

ensure dust particles settle on the roof are cleaned away first, a small sedimentation tank

that helps to settle some fine particles, a filter mechanism at the entry point to trap large

particles and cleaning of gutters to remove leaves, bird nests and other trapped object

before rainy season.

40 | P a g e

3. Water should be first be disinfected before used for drinking. The disinfection may be as

simple as boiling the water or use of locally available chlorine disinfection such as water

guard.

4. Although it was established that underground water is plenty in Syokimau, the yield may

vary in different time of the year and increase of number of boreholes in the area. Therefore

on should only pump what they need so as to avoid deplenishing the underground water

storage.

5. One should constantly evaluate the water quality of the borehole so as to ensure that the

water obtained from this source is safe for drinking. Ground water quality greatly vary

from time to time and therefore only periodic water quality check will determine how safe

the water is.

6. Further studies should be undertaken to establish extent of pollution of underground water

and variation of water tables.

7. A cost evaluation should also be carried out for both sources so as to establish the most

economical alternative source of water in Syokimau.

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REFERENCES

1. Ministry of Water and Irrigation (2005) Design and Practice Manual for Water Supply

Services in Kenya

2. Andrew D. Eaton, Mary Ann H. Franson (2005) Standard Methods for the Examination

of Water and Wastewater 21st ed. Washington, DC: American Public Health Association,

American Water Works Association & Water Pollution Control Federation

3. World Health Organization (2011) Guidelines for drinking-water quality, fourth edition

4. Kamala A, Rao K (1988) Environmental Engineering; Groundwater Sources and Quality

pp 17-29. Published by Tata McGraw Hill Publishing Company Ltd

5. Criteria and Guidelines for the "Rainwater Harvesting” Colorado Water Conservation

Board (2010)

6. Elizabeth M. Shaw (1994) Hydrology in Practice, Third Edition, London, Chapman &

Hall

7. H.M Raghunath (2006) Principle-Analysis-Design, Revised Second Edition, New Age

International, New Delhi

http://www.who.int/water_sanitation_health/publications/2011/dwq_guidelines/en/index.html

http://cwcb.state.co.us/legal/documents/guidelines/finalrainwaterpilotcg.pdf

42 | P a g e

APPENDICES

APPENDIX A: SYOKIMAU AREA (STUDY AREA)

(Source: Google Maps Data – 2014)

Figure A-I: Boundary Map of Syokimau Area

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Figure A-II: Residential Houses in Syokimau

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Figure A-III: Water Harvesting System Practiced in Syokimau

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Figure A-IV: Elevated Water Tanks for Estates Next to Boreholes in Syokimau

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APPENDIX B: WATER CONSUMPTION RATES

Consumer Unit Rural Areas Urban Areas

High

Potential

Medium

Potential

Low

Potential

High

Class

Housing

Medium

Class

Housing

Low

Class

Housing

People with

individual

Connection

Liters/head/day 60 50 40 250 150 75

People without

connection

Liters/head/day 20 15 10 20

Livestock unit Liters/head/day 50 -

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APPENDIX C: RAINFALL DATA

(Source: JKIA Meteorological Station, Station ID: 9136168, Kenya Meteorological Department)

YEAR JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

1990 27.1 40.9 179.1 167 556 3.2 5.3 56 17.6 0 173 94.9

1991 9.6 0 98.5 0 209.3 15.6 1.8 6.9 2.4 35.2 841 95.9

1992 3.4 10.2 9.1 228.3 155 12.7 35.7 9.7 0.4 37.7 86.4 132.6

1993 210.9 51.7 17 8.3 51.4 43.2 0 4.1 0 69.7 68.6 83.2

1994 0.6 97.2 48.6 163 58 35.7 3.1 23.7 0 73.1 203 28.1

1995 59.1 79.4 133.3 70.7 86.5 46.9 18.1 17.5 32.3 45.6 29.5 32.4

1996 36.9 69.4 55.8 61.2 55.8 58.5 16.3 12.1 2 0 129 10.6

1997 0 0 35.2 235.6 163.2 6.6 14.7 0 0 308 308 124.9

1998 322.6 125 74.2 110.4 322.5 69.9 31.3 6.2 18.9 0 74.2 6.4

1999 0 1.3 123.5 91.6 3 1.9 3.9 32.9 0 37.9 251 95.9

2000 13.4 0 18.5 74.8 18.7 26.9 1 1.4 8 11.6 113 37.4

2001 306.5 10.7 161.3 67.2 38.3 13.7 19.9 14.3 3.7 33.6 199 15.9

2002 57.6 15.1 99.1 151.9 158.9 0.8 0.2 3.9 54.5 48.7 115 331.2

2003 16.9 9.5 22.1 154.6 229.8 6.8 1.6 47.8 40.8 52.3 120 25.2

2004 33.7 76.2 93.3 137.6 57.9 2.9 0 0.6 26.5 65.3 125 0.4

2005 36.7 1.4 46.3 130.2 89.5 3.7 11.7 0.3 9.1 6.6 65.5 1.2

2006 5.2 38 124.5 222.9 98.2 0.2 0 27.8 5.5 0 233 19.2

2007 83.4 18.2 35.8 195.7 52.8 27.2 18 12 19.6 23.7 95 0

2008 51.3 24.1 193.2 81 4.7 1.5 27.2 3.2 35.4 101 82.6 0

2009 52.4 34.1 27.1 84.5 140 36.6 5 0.6 2.3 65.6 48.6 112.7

2010 68.9 96.7 132.1 54 81.1 26.6 1.3 6.6 13.9 34.9 77.5 55.7

2011 1.8 74.8 92.7 17.8 44.5 29.6 2.9 42.2 27.8 46.9 250 29.1

2012 0 2.4 5.2 288.8 199.6 32.2 13.4 3.8 36.3 63.7 64.8 259.1

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APPENDIX D: BOREHOLE DATA FOR SYOKIMAU

(Source: Water Resource Management Authority – Nairobi Regional Office)

UTM

Total

Depth Struck

Rest

Test

Yield

Owner X Y Z Permit No BH No (m) (m) (m) (lpm)

Maryanne

Muchui 270,895 9,849,768 1,615 WRMA/ACB/6381

David Wambua

Mila 270,726 9,850,212 1,618 WRMA/ACB/6506

Agnes Kariuki 269,589 9,849,291 1,616 WRMA/ACB/6898

Thomas Musau

/ Mumwa

Solutions

271,793 9,849,886 1,612 WRMA/ACB/347

Mastermind

Tobacco 269,502 9,848,532 1,607 WRMA/ACB/3227

Apex Steel

Limited 272,267 9,850,189 1,608 WRMA/ACB/751

C-

15088

S S Mehta 269,282 9,850,488 1,619 WRMA/ACB/3430

George Kinyua 269,643 9,850,882 1,618 WRMA/ACB/702 C-

15222 200 156 96.09 176.7

Faulu Pamoja /

Wachuka

Waruigi &

Partners

271,717 9,851,030 1,613 WRMA/ACB/526

175 114 96 200

Andrew

Wanyoike 268,602 9,849,488 1,628 WRMA/ACB/6905/8

182 128

100

Kenya Slum

Upgrading

Programme

270,845 9,847,300 1,609 WRMA/ACB/6225

Viswa Builders

Ltd. 268,623 9,848,944 1,627 WRMA/ACB/11598

C-

12707

Parbat Siyani

Construction

Limited

270,435 9,847,139 1,624 WRMA/ACB/6423

SYOKIMAU

CDF PROJECT 272,843 9,850,437 1,615

Mavoko CDF

Project-

Syokimau

272,846 9,850,434 1,612

All Pack

Industries 270,199 9,847,132 1,617 WRMA/ACB/669

C-

10291 154 146 107 167

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APPENDIX E: WATER QUALITY STANDARDS

PARAMETERS UNITS WHO

STANDARDS

KEBS

STANDARDS

pH pH Scale 6.5-8.5 6.5-8.5

Colour TCU Max 15 Max 15

Conductivity μS/cm Max 2500 Max 2500

Iron mg/l Max 0.3 Max 0.3

Turbidity NTU Max 5 Max 5

Chloride mg/l Max 250 Max 250

Total Hardness mg CaCO3/l Max 500 Max 500

Alkalinity mg CaCO3/l Max 500 Max 500

Dissolved Oxygen mg/l - -

Nitrate mg/l Max 10 Max 10

Total Suspended

Solids

mg/l Max 1500 Max 1500

Dissolved Solids mg/l Max 1500 Max 1500

Fluoride mg/l Max 1.5 Max 1.5

Coliform Colonies/ml 100 100

comparison of water harvesting with borehole...

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