chapter 4

Chapter 4Water Supply

Will Our Taps Run Dry?

Think about this!

Chapter 4 Water Supply• In this chapter, you will explore these Guiding

Questions:1. What is water shortage?2. Which locations in the world are facing water

shortage?3. Why does water shortage occur?4. How does water shortage impact people and

countries?5. How can Singapore avoid water shortage?

1. What is water shortage?Hydrological cycle (water cycle)• Continuous movement of water from the earth’s

surface to the atmosphere and back again. Along the way, the water takes on different states

• Water cycle is driven by heat energy from the sun

Water is a renewable resource — can be naturally replenished

1. Heat from the sun causes water from lakes, rivers, oceans and the surface layers of soil to change to water vapour (evaporation)

1. Plants also give out water vapour through their leaves (transpiration)2. As the water vapour rises into the atmosphere, it cools and becomes water droplets (condensation)

3. These water droplets gather together to form clouds. When more water droplets gather, the clouds get too heavy. Thus, water falls back to the earth’s surface (precipitation)

4. Some of the water that falls onto the ground may seep into the soil (infiltration). Water that infiltrates deep into the ground, and is contained in the soil and the underlying rocks, becomes groundwater.

5. The rest of the water that is not absorbedinto the ground flows over the earth’s surface, down hills and mountains into rivers, lakes and eventually seas (surface runoff)

Hydrological cycle

1. What is water shortage?Uses of water• Domestic use– Cooking, cleaning– Drinking

• Economic activities– Agriculture: 20% of total

water to grow rice, 3% of total water to grow cotton

– Industry: To generate electricity and manufacture products

1. What is water shortage?Uses of waterDomestic use• Globally, domestic water use accounts for the

smallest percentage of all water used• Domestic use– Consumption (e.g. drinking and cooking)– Hygiene (e.g. bathing and flushing the toilet)– Amenity use (e.g. washing the car and watering the

garden)

The volume and way that water is used may differ from household to household

1. What is water shortage?Domestic use (Singapore)

1. What is water shortage?Domestic use (Canada)

1. What is water shortage?Uses of waterEconomic use (Agriculture)• Uses the greatest amount of water globally• As the world’s population grows rapidly, more water

is needed to grow more crops to feed people• Crucial for growing fruits, vegetables, grain, coffee,

tea, oil palm, rubber and cocoa• In places with abundant rainfall all year round less water is used for agriculture because crops are naturally watered by rain

1. What is water shortage?Uses of waterEconomic use (Agriculture)• Where rainfall is low or irregular more water is used for agriculture because of irrigation

• Irrigation: Water is obtained from water bodies (rivers, lakes, reservoirs and wells) and is sprayed or watered onto crops

• Without irrigation, crops will not grow in dry areas such as the deserts of California

1. What is water shortage?Uses of waterEconomic use (Agriculture)

Often, large amounts of water are needed to produce a small quantity of an agricultural product

1. What is water shortage?Uses of waterEconomic use (Agriculture)• To meet the world’s increasing demand for food,

more places are relying on irrigation• More water is used to increase crop yield• Compared to 50 years ago, the amount of water

used for irrigation today has increased by 70 %• Area of irrigated land has also doubled

1. What is water shortage?Uses of waterEconomic use (Industry)• Industrial water use accounts for 22 % of total water

used– 57–69 % is used for hydropower and nuclear power

generation– 30 –40 % is used for industrial processes such as

manufacturing– 0.5–3 % is used for thermal power generation

• Major users of water are industries that produce steel, chemicals, paper and petroleum

1. What is water shortage?Uses of waterEconomic use (Industry)• Used in all manufacturing processes as the processes

create lots of heat due to friction and chemical reactions

• Needed to cool down the machinery and equipment

• Used to clean the machinery and products

1. What is water shortage?Uses of waterEconomic use (Industry)• Power generation– Large amounts of water are used for the

manufacture, maintenance and cooling of generators– Large portion of water is lost through evaporation,

absorption and leaks• Thermal power generation– Electricity is produced by steam-powered generators

where huge amounts of water are required to produce the steam

1. What is water shortage?Uses of waterEconomic use (Industry)• Some industrial products are used as raw materials for

making other products• Thus, more water is needed to produce the finished

product

1. What is water shortage?Uses of waterEconomic use (Industry)• Tourism industry– In 2012, there were 1.035 billion international visitors – Estimated that the number of international visitors will

reach 1.8 billion by 2030– With steady expansion of the global tourism industry, the

demand for water will increase

1. What is water shortage?Uses of waterEconomic use (Industry)

1. What is water shortage?Water footprint• Water footprint: Total volume of water (m3) used to

produce the goods and services for a person in a year which includes all domestic and economic uses of water

• Water per capita: Amount of water used per person• Some countries have a bigger water footprint as

they use a lot more water per capita than others

1. What is water shortage?Water footprint

1. What is water shortage?Water shortage• Water shortage: Occurs when the level of water

usage exceeds the water supply available(water is being used at a rate faster than it can be replenished)

• Not everybody has access to clean water• Over 1 billion people in the world do not have

enough clean water to drink and this number is predicted to increase

1. What is water shortage?Water shortageExample (New Delhi, India) • Faces water shortage due to the country’s growing

population whereby a large number of people has moved from the countryside to the city

• Water demand in peak summer months has reached more than 4.35 million m3 a day

• However, the city gets only about 3.22 million m3 a day

1. What is water shortage?Water shortage

2. Which locations in the world are facing water shortage?

Distribution of water on earth• Water is the most abundant substance on earth’s surface• 71 % of the earth’s surface is covered in water where

most of the earth’s water is in the oceans• Only 2.8 % of the earth’s water is fresh water which is

found in rivers, lakes and groundwater, in which– 68.6 % is locked up in ice caps and glaciers– 30.1 % is groundwater– 1.3 % is on the surface of the earth, in which

• 87 % is in lakes• And the rest is found in rivers and swamps


Distribution of water on earth


Distribution of water on earthOceans• The world’s oceans are all interconnected in a single,

enormous body of water• Pacific Ocean is the largest, covering 1/3 of the total

area of earth’s surface• Water in the oceans is replenished by precipitation

and rivers that flow into the oceans


Distribution of water on earthOceans


Distribution of water on earthGroundwater• Is stored underground in the soil and underlying rocks• When rain falls to the ground, some of the water

infiltrates the ground until it reaches solid rock• The water then fills up the empty spaces and cracks

above that layer of rock• When all these spaces are entirely filled, the ground is

filled with water. This water is groundwater.• As more water infiltrates deep into the ground,

groundwater storage will increase


Distribution of water on earthGroundwater


Distribution of water on earthGroundwater• People mostly use surface fresh water however,

people are increasingly drawing from groundwater in places where there is insufficient surface fresh water– Many countries use groundwater for irrigation– Globally, about 38% of water for irrigation comes from

groundwater– Countries with the largest areas irrigated with

groundwater are India (390,000 km2), China (190,000 km2) and USA (170,000 km2)


Distribution of water on earthIce caps, glaciers, rivers and lakes• Ice cap: A thick, continuous mass of ice which covers

large areas of land• Glacier: A body of ice that moves down a slope due

to gravity. It forms when snow accumulates and is compacted to form ice

• Almost 69% of the earth’s fresh water is trapped in ice caps and glaciers


Ice caps and glaciers are usually far from where people stay and hence inaccessible


Distribution of water on earthIce caps, glaciers, rivers and lakes


Distribution of water on earthIce caps, glaciers, rivers and lakes• River: A large natural stream of fresh water flowing

along a definite course into another water body• Source may be a lake, spring or melting glacier• As the river flows downstream, precipitation,

groundwater and other smaller streams (tributaries) add to the flow

• The end of a river is its mouth where it flows into another body of water such as a lake or the ocean


Distribution of water on earthIce caps, glaciers, rivers and lakes• Lake: A body of water occupying a hollow in the

earth’s surface

The Great Lakes of North America is the largest group of freshwater lakes on earth


Locations in the world facing water shortage• Fresh water is distributed unevenly across the

world• Fresh water availability of a country is calculated

by dividing the country’s total water resources (m3) by its total population

• Different levels of fresh water availability: Water security, water vulnerability, water stress, water scarcity


Locations in the world facing water shortage• Water security: When a country has adequate and

sustainable fresh water for human consumption and use more than 2,500 m3 per capita per year

• Water vulnerability: If fresh water availability is between 1,701 and 2,500 m3

• Water stress: If fresh water availability is between 1,001 and 1,700 m3

• Water scarcity: When fresh water availability falls below 1,000 m3


Locations in the world facing water shortage


Locations in the world facing water shortage• Northern Africa is one of the driest areas in the

world • Rainfall is low and unreliable (natural factor)• Most countries in Northern Africa cannot meet their

current water demand• Forecasts show that climate change will make the

weather hotter and drier — more water will be lost due to higher evaporation rates and reduced infiltration smaller groundwater supply


Locations in the world facing water shortage• Water shortage can also be caused by human

activities

For example, • Uzbekistan (in Central Asia) used to rely on abundant

water supply from the Aral Sea (once the world’s fourth-largest lake)– Due to increasing demand for crops, the increase in

irrigation led to a decreasing supply of water Causing water shortage in surrounding countries


Locations in the world facing water shortage


Locations in the world facing water shortage• Since 1950s: People have diverted water from the

rivers that flow into the Aral Sea to large-scale irrigation projects for crops such as rice and cotton

• By early 1980s: Aral Sea’s water supply was completely cut off and Aral Sea began to shrink drastically

• By 2006: Aral Sea had dried up to almost 10% of its original size as the Aral Sea is a closed lake and it has no outlet

• Over time: Remaining water in the sea has become salt water and thus less suitable for drinking

3. Why does water shortage occur?

Demand factors• Population growth• Affluence

Supply factors• Seasonal rainfall• Water pollution


Demand factorsPopulation growth• Ever-increasing world population• Increasing demand for food• Water consumption for agriculture will increase• Worldwide demand for water is doubling every 21

years, or even faster in some countries• Water supply cannot keep up with such demands


Demand factorsPopulation growth


Demand factorsPopulation growth• Most of the world’s population

growth will take place in less developed countries

• These countries are already facing water shortage or water stress

• Rising populations in these countries will put an even greater strain on their water resources


Demand factorsPopulation growthExample• Shijiazhuang (a growing city in China) is experiencing

water shortage due to its rising population– In 1900: Consisted of a group of farming villages– In 2007: City had about 2.3 million people

• Rising population Increasing demand for water • The city now pumps groundwater heavily with some

of the wells going as deep as 200 m


Demand factorsAffluence• Being affluent: Having wealth and being able to live more

comfortably• Water consumption has increased twice as fast as

population growth in the last century • People living in affluent countries use more water, or

have a greater water footprint, than those in less developed countries

• Between 2007 –2025, water consumption is predicted to rise by 50 % in less developed countries and 18 % in developed countries


Demand factorsAffluence

• With more money, people may also start to consume goods that are produced using more water and live a lifestyle that consumes more water


Supply factorsSeasonal rainfall• In Singapore, the

amount of rainfall is generally the same every month and the annual precipitation is more than 2,000 mm

3. Why does water shortage occur?Supply factorsSeasonal rainfall• In some countries, however, rainfall can vary greatly from

month to month which affects the supply of fresh water available for use

Example (India)• High annual precipitation of

more than 1,200 mm• Rainfall is unevenly

distributed throughout the year• Most rainfall is received between

June and September (southwest monsoon season)

3. Why does water shortage occur?Supply factorsSeasonal rainfallExample (India)• More than ½ of India’s population are engaged in farming• Timing and amount of rainfall are crucial for the harvesting of crops

(boom or a bust for India’s economy)• In 2009:

– Monsoon rains did not come on time– Widespread drought where the sugar production was so low that India had to

import sugar• In 2012:

– Monsoon rains were below average in the first half of the season– Large parts of the country (including New Delhi) experienced drought– Heavy rains eventually came in August but it was too late for many rain-

dependent farms


Supply factorsSeasonal rainfall• Irregular distribution of rainfall throughout the year

in some regions will be intensified by climate change • Climate change: Variation in the global climate or

climatic pattern in the long run. • Earth’s average temperature is predicted to rise

which will cause a change in rainfall patterns and more extreme weather-related hazards such as floods and drought


Supply factorsWater pollution• Pollution: Introduction of substances into the natural

environment (air, water, land) that results in unpleasant or damaging effects to the environment and human health

• Common pollutants include garbage, chemicals and waste water

• Can cause the water quality to drop, sometimes becoming unusable for people and unsuitable for aquatic life

• Supply of clean fresh water is reduced and water shortage may occur


Supply factorsWater pollution


Supply factorsWater pollutionExample (Ganges River)• Largest river in India • More than 400 million people live along the river (most

populated river basin in the world• River provides water for

drinking, bathing and irrigation• Also, it holds spiritual significance

as it is seen as a sacred river• Pollution has threatened this

water resource

3. Why does water shortage occur?Supply factorsWater pollutionExample (Ganges River)• Industries near the river have inadequate waste treatment

facilities and dump their waste directly into the river• Large concentration of leather industries in Kanpur city use

large amounts of chromium and other chemicals in the leather tanning process and discharge the waste products into the river

• Surrounding towns also discharge a large amount of waste into the river

• As a result, the water has turned brown• Kanpur is facing water scarcity due to the unclean water

3. Why does water shortage occur?• In many places, water shortage is caused by both

natural and human factors• Many people spend a large proportion of their time

searching for clean water

There are serious consequences to lacking such an essential and precious resource!

4. How does water shortage impact people and countries?

Domestic impact• Increased difficulty in collecting water• Water rationing

Economic impact• Reduced agricultural yields• Increased cost of industrial production

Political impact• Conflict over water supply


Domestic impactIncreased difficulty in collecting water• 1.1 billion people lack access to safe drinking water• In the less developed countries, one in five people do

not have access to safe water• In most of these countries, 90 % of water is used for

agriculture, leaving little for domestic use• Drought can also cause wells and ponds to dry up


Domestic impactIncreased difficulty in collecting water• Water is scarce and people

have to travel long distances to obtain it

• On average, women in some parts of Asia and Africa have to walk 6 km to collect water

• They can only bring back as much as they can carry and the water collected may be dirty


Domestic impactWater rationing• Water rationing: Making water available only at certain times

of the day• During the 1960s, Singapore suffered a severe drought which

caused water levels in the reservoirs to be dangerously low• Singapore’s water supply was under huge stress• To conserve the water supply, the government imposed water

rationing which affected every household in Singapore• People had to queue to collect water for their daily use during

the water rationing exercise


Economic impactReduced agricultural yields• Agriculture uses 70 % of the global fresh water

supply• If water supply decreases, crop yield (the amount or

quantity grown) drops • Less food will be produced and some people may die

from starvation


Economic impactIncreased cost of industrial production• Cost of industrial production: The cost of producing

and manufacturing goods• Fresh water is needed by industries for various

purposes • As water constraints increase, so will the cost of

industrial production


Economic impactIncreased cost of industrial productionExample (Power generation industry)• The power generation industry relies heavily on water to

cool parts of the generators• In Europe and USA, droughts have caused water

shortages and warmer waters• As a result, during warm, dry summers in 2003, 2006 and

2009, some power plants in Europe reduced their power output as there was a lack of water to cool the generators


Economic impactIncreased cost of industrial productionExample (Power generation industry)• Similarly, from 2007 to 2008,

several power plants such as the Millstone Nuclear Power Plant in the US had to cut production or shut down for a few days

• The cut in power production increased the price of power and affected the cost of production in other industries


Economic impactIncreased cost of industrial productionExample (Beverage industry)• Companies which produce soft drinks use a lot of water in

their production• Besides being the main ingredient, water is also used in other

parts of the process such as rinsing, cleaning, heating and cooling

• 1 litre of soft drink requires at least 2.43 litres of water to produce

• An increase in water prices will lead to higher production costs


Political impactConflict over water supply• Conflict can arise over water resources when there is not

enough water to go around• On a local scale, there can be conflicts between farmers

and factories over the use of water in a lake• On a national or global scale, problems may arise when

states or countries tap into the same water resource• One country’s use of the resource could reduce the

amount available to another country e.g. Mekong River


Political impactConflict over water supply• The Mekong River winds its way

nearly 4,500 km through six countries• From its source on the Tibetan

Plateau, the river meanders through China, Myanmar, Lao PDR, Thailand, Cambodia and Vietnam before reaching the South China Sea

• The river supports 60 to 70 million people in Southeast Asia and southern China


Political impactConflict over water supply• With increasing demands for water, conflicts may arise

among countries that share the same global ‘well’

For example:• Lao PDR’s proposal to build the Xayaburi hydropower

dam received strong objections from neighbouring countries as the dam will decrease the flow of water downstream

• Livelihoods of many who rely on the river to maintain their fisheries and farmland could be affected

5. How can Singapore avoid water shortage?

We never know the worth of water till the well is dry.

Thomas Fuller,Writer


• Water is a scarce and precious resource in Singapore• Despite having high total annual rainfall of 2357.8

mm, there is little land to capture rainfall for use by its people and industries

• By looking to technology for solutions, Singapore today is a world leader in sustainable water resource management (planning and distributing water resources so that they will not be used up)


Reduce water consumption• Pricing of water• Public educationIncrease water supply• Local catchment water• Imported water (from Johor)• NEWater• Desalinated waterConserve through protecting water resources• Protection of water resources


Reduce water consumptionPricing of water• Water in Singapore is priced to reflect the scarcity of

water and to cover the high cost of producing clean water

• Water Conservation Tax: Pricing system where an additional amount of money is charged based on total water consumption

• Pricing system encourages people to reduce their water consumption


Reduce water consumptionPricing of water

Water is being priced higher when the consumption amount is greater


Reduce water consumptionPricing of water• To ensure that all Singaporeans have access to clean

water, the government provides a U-Save rebate• This sum of money help offset the utility bills for

lower-income families• Approach demonstrates that water does not need to

be under-priced to ensure access for all


Reduce water consumptionPricing of waterAdvantages• Allows people to be more mindful of their water

consumption• Reflects the cost of producing clean water People can appreciate the value of clean water


Reduce water consumptionPricing of waterDisadvantages• For industries that use a lot of water, it increases

their total cost of production which may be passed on to consumers

• May not affect those who can afford the higher price May continue to use any amount of water they want


Reduce water consumptionPublic educationWater Efficiency Labelling Scheme (WELS) • Scheme was started by PUB in 2009 to educate the

public on water conservation through using water-efficient appliances

• WELS is a grading system which uses ticks to indicate the water efficiency level of a product

• More ticks indicate greater water efficiency


Reduce water consumptionPublic education• Allows consumers to make

informed choices when purchasing household products such as washing machines

• Helps public to be more aware of reducing water consumption by using more water-efficient products


Reduce water consumptionPublic educationPUB’s water-saving kit • Includes a set of thimbles (a cap that can be placed

on taps) with three or four holes• Thimbles allow residents to control the rate of water

flow from their taps• Kit also comes with a set of Water Wally stickers that

have messages on how to save water in homes


Reduce water consumptionPublic educationAdvantages• Can teach many people about the importance of

water in their lives• Has the potential to make lasting positive changes in

people’s use of water


Reduce water consumptionPublic educationDisadvantages• Takes time to change people’s behaviour• Success of public education depends on whether

people want to change their behaviour


Increase water supplyLocal catchment water• Surface catchment: Area over which rain falls and is

collected• Singapore is a small island without natural lakes,

significant groundwater supplies, or large land areas to collect rainwater

• Rainwater collects in rivers, streams, drains, canals and stormwater collection ponds, and is channelled to reservoirs where it is stored


Increase water supplyLocal catchment water• Surface catchments provide ½ of the country’s water

needs • There are now 17 reservoirs with the addition of Marina

Reservoir, and the Serangoon and Punggol reservoirs(increase to 2/3 of the country’s land area)

• By 2060, PUB plans to harness water from the remaining streams near the coastline, bringing the total surface catchment area to 90 % of the total land area


Increase water supplyLocal catchment waterAdvantages• Take advantage of Singapore’s high rainfall• Catchment areas can also be recreational places


Increase water supplyLocal catchment water


Increase water supplyLocal catchment waterDisadvantages• Less land is available for other uses such as housing

and industry• When there is little rainfall or a drought, local

catchment areas are ineffective


Increase water supplyImported water• In 1927, Singapore signed its first agreement with

Johor to import water• Pipelines were built to transport water from Johor to

Singapore • Currently one existing water agreement which

secures Singapore’s water supply from Malaysia until 2061


Increase water supplyImported water• Importing water is not a long-term solution• Singapore has been working on increasing the size of

its local water catchment areas• More reliable water supply from non-conventional

sources (NEWater and desalinated water) have been established

• Singapore could be self-reliant in its water supply by 2061


Increase water supplyImported waterAdvantages• Does not require land and hence frees up the land

for other uses• Is a cheaper source of water compared to

desalinated water or NEWater


Increase water supplyImported waterDisadvantages• May not be enough to meet water demands• Water agreements will eventually expire and there

are no guarantees of future agreements


Increase water supplyNEWater• Used water may be treated to become drinking water • Result of clever planning and technology where fresh

water can be used more than once• Used water becomes a new source of water


Increase water supplyNEWater• Ideal for use in certain industries as it is purer than tap

water• Currently, supplied mainly to wafer fabrication plants,

electronics factories and power plants• A percentage of NEWater is mixed with raw water from

the reservoirs and treated at the waterworks• Currently meets 30 % of Singapore’s water demand• The existing plants will be expanded by 2020 where it is

expected to meet 40 % of Singapore’s water needs and 50 % of Singapore’s future water demand by 2060


Increase water supplyNEWater• Public was concerned about the idea of treated used

water when it was first launched• Public’s confidence have since been strengthen• Public is being educated through the NEWater Visitor

Centre– Can view the technology used to produce NEWater and

sample bottled NEWater


Increase water supplyNEWaterAdvantages• Not dependent on rainfall because it is produced

from used water• Ultra-pure and of high quality, which the wafer

fabrication industry in Singapore has found suitable for their use


Increase water supplyNEWaterDisadvantages• Expensive to produce• Public may find it difficult to fully accept this new

technology of obtaining water from used water due to lack of knowledge about the treatment process


Increase water supplyDesalinated water• Desalination: Process of removing dissolved salts (such

as sodium chloride) and other minerals from water– Step 1: Seawater goes through a pre-treatment process

where suspended particles are removed– Step 2: Reverse osmosis technology is employed– Step 3: The desalinated water is blended with treated water

before it is supplied to homes and industries• The two desalination plants (SingSpring and Tuaspring)

aim to meet 30 % of Singapore’s water demand by 2060


Increase water supplyDesalinated waterAdvantages• Independent of rainfall and can be used to

supplement water supply during a long dry spell• Attractive since Singapore is an island and is

surrounded by a limitless supply of seawater


Increase water supplyDesalinated waterDisadvantages• Very expensive to produce as the production is

energy-intensive • Large amounts of chemicals and salt solutions are

produced during the desalination process and if they are improperly disposed of into the oceans, it may result in pollution


Conserve through protecting water resourcesProtection of water resourcesIndividual• Everyone has a part to play in conserving water and

keeping waterways clean in Singapore• We can help by keeping drains and canals in our

catchment areas clean• Protection of waterways is only possible when the

community values water


Conserve through protecting water resourcesProtection of water resourcesActive, Beautiful, Clean Waters (ABC Waters) programme• Programme was launched by PUB in 2006 to

promote the enjoyment of Singapore’s waters• Parks have been built near water bodies for all to

enjoy• Selected reservoirs and rivers have been opened for

various recreational activities and water sports such as kayaking, wakeboarding, rowing and sailing


Conserve through protecting water resourcesProtection of water resources‘Friends of Waters’ programme • Outreach programme by PUB which encourages the

public to care for our waterways• Schools, private and nongovernmental organisations

can be a ‘Friend of Water’ when they adopt a waterway, conduct cleanups and help monitor its cleanliness

• Contribute to raising awareness about protection of our water resources


Conserve through protecting water resourcesProtection of water resourcesABC Waters Learning Trail • Consists of a series of outdoor, place-based trails

where students can learn about Singapore’s water story, heritage of water sites and unique design features that help cleanse water naturally

• Students can also volunteer as a trail leader to help raise awareness about water management and appreciation for water resources


Conserve through protecting water resourcesProtection of water resourcesAdvantages• A cost-effective method to ensure clean water • When everyone plays their part to keep waterways

clean, everyone in turn enjoys a clean and healthy environment


Conserve through protecting water resourcesProtection of water resourcesDisadvantages• Dependent on effective public education • Dependent on the cooperation of everybody

ConclusionWater is essential for living.

There is an urgent need to protect our world’s water resources to ensure that they do not run out and that

everybody can get clean, fresh water.

All of us have a role to play in conserving and valuing our water resources while we enjoy using it.

We can share what we have learnt with family and friends, practise good water-saving habits and keep

the waterways clean.

chapter 4

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