Dr Rajiv Desai

THE WATER

January 23, 2010 by Dr Rajiv Desai

THE WATER :
Water is defined as a ubiquitous chemical substance having 2 hydrogen and 1 oxygen atoms bonded to form a molecule H2O, also known as hydrogen oxide.Deuterium is an isotope of hydrogen which combines with oxygen to form heavy water(D2O).
Water is essential for survival of life as well as essential for economy,industry,ecology,climate cycle and agriculture.
60 % of human body and 80 % of human brain is water.Adult human needs 2 to 3 liters of water daily for drinking and a human can not survive for more than few days without drinking water.75 % of all people in the world are chronically dehydrated leading to day-time fatigue,cancer risk,poor mental ability and body pains.Minimum water requirement per person per day is 50 liters for drinking,bathing,cooking and sanitation.America/Canada uses 2 to 8 times more water per person than most developing nations.Civilisations have developed around water sources/rivers.
Water refers to its liquid state but its solid state is known as ice and gaseous state is known as vapor/steam.Water is formed as a bye-product of star formation in the universe.Water exists on other planets of solar system as vapor on Mars,Venus,Jupiter and Mercury and as ice on Saturn.Even other galaxies of the universe are likely to possess water because hydrogen and oxygen are the most abundant elements in universe and therefore life is likely to exist in other galaxies.When astronauts saw earth from moon,it looked blue because 71 % of earth’s surface is covered with ocean water and when visible light passes through water, the blue light is transmitted better than the red light giving water a faint blue colour.Water exists on earth in the form of surface water and ground water.The surface water is in oceans,rivers,lakes,streams,and reservoirs etc and ground water is underground in aquifers,water sheds and springs.
Water fit for human consumption is called drinking water or potable water.1 out of 3 people in the world does not have enough water to meet daily needs and is in water stress.Due to population growth,water consumption will increase by 40 % in the year 2025 when 2 out of 3 people will live in water stress.Ironically,the rainfall throughout the world has been adequate but what has gone wrong is water management.Water scarcity forces people to use unsafe water for drinking/bathing/cooking.Unhygienic water leads to diarrhea,typhoid,cholera,jaundice and dysentery.Water scarcity forces people to store water causing mosquito breeding which results in malaria,dengue and filariasis.5 to 10 million deaths occur due to waterborne diseases every year worldwide.In fact,waterborne diseases cause the occupancy of half of all hospital beds and loss of 443 million school days annually worldwide.Water scarcity leads to use of wastewater for agriculture and 10 % world population eats food irrigated by wastewater containing disease producing microorganisms/toxins/chemicals.In underdeveloped countries,90 % of wastewater is discharged in rivers/lakes making it difficult to find potable water.GDP per capita has direct correlation with access to safe drinking water.Even in America,1 out of 10 people drinks polluted water despite clean water act passed 4 decades ago.The clean water act was violated 500000 times in last 5 years by american industry.Each glass of tap water contains 10 million bacteria in it.Water scarcity occurs even in those areas where there is plenty of rainfall/fresh water.The demand and supply balance is based on how water is conserved,used,distributed as well as quality of water.
Water measurements :
1 cubic centimeter of water = 1 milliliter of water
1000 cubic centimeter of water = 1 liter of water = 1 kilogram of water
1 cubic meter of water = 1000 liters of water
1 cubic kilometer of water(ckm) = 1000 billion liters of water
Sea water is heavier than fresh water because it contains 3.5 % salt dissolved in it.1 kg of sea water contains 35 gms of salt in it.1 liter of sea water weighs 1.03 kg.The salt to sea water comes from breaking up of rocks and wearing away of mountains releasing salts that are washed down by rain water and also from rocks at the bottom of sea.The total amount of salt in all oceans is 50 million billion tons and if all the salt is removed from ocean and spread on earth’s land surface,it will be 500 feet thick.Fresh water contains less than 0.05 % of salt in it.Humans can not survive on sea water because it requires more water to excrete excess salt through kidney than the water available from sea water and hence a person drinking sea water will develop high sodium level in blood causing death.Also,sea water is not suitable for agriculture and industry.
The total amount of water on earth is 1400 million cubic kilometers(ckm); out of which only 2.5 % fresh water(35 million ckm) and 97.5 % sea water(1365 million ckm). Out of 35 million ckm of fresh water on earth,24 million is ice/snow, 8 million is ground water and rest as rivers/lakes.
Total usable fresh water available for humans/ecosystem is 200000 ckm which is less than 1 % of total fresh water resources and less than 0.02 % of total water on earth.Fresh water sources are unevenly distributed on the earth with Canada having 20 % of fresh water with 0.5 % world population and China having 7 % of fresh water with 21 % world population.Agriculture consumes 75 % of fresh water,industry 20 % and remaining 5 % fresh water consumed by domestic household.The wasteful agriculture and irrigation practices are the root cause of water scarcity despite adequate rainfall.Ground water represents 90 % of world’s readily available fresh water sources which caters to need of 1.5 billion people for drinking water.Glaciers are large sheet of ice that flow down very high mountains.10 % of earth’s land area is covered by glaciers which store 75 % of world’s fresh water. If all the ice of all the glaciers were to melt, the sea water level would rise by 70 meters.
Regional water scarcity means the water usage exceeds the annual natural water replenishment from water cycle and is defined as less than 1700 cubic meters of fresh water available per capita per year which comes to 4657 liters of fresh water per capita per day for human consumption including domestic,industrial and agriculture use.Due to rapid population growth,12000 cubic meters of fresh water available per capita per year in the year 1970 fell to 7000 cubic meters in the year 2000 and will reach 5000 cubic meters in the year 2025.However,since fresh water is unevenly distributed,densely populated Asia/Africa may get only 1200 cubic meters of fresh water per capita per year in the year 2025 resulting in water scarcity among 3 billion people.Water scarcity leads to food shortage,famine and starvation.
Causes of water scarcity includes population growth,food production,climate change,poverty,water pollution,water demand,land use,poor water management,socio-political issues etc.
WATER CYCLE:
Water cycle is defined as a journey/movement of water from ocean/land to atmosphere and back again.The earth has a limited fixed quantity of water and the same water keeps on going around and around and around in water cycle.Water cycle replenishes water continuously.Solar heat provides the energy for water cycle.The solar heat evaporates water from ocean/river/lake to atmosphere as vapor and also trees release water by traspiration as vapor. Water vapor cools down in atmosphere and condenses as clouds and when clouds supersaturate, water is precipitated on earth as rain/hail/snow/sleet/dew/frost etc.The world’s average rainfall is 850 mm every year.The fallen water is collected in ocean/river/lakes as well as soaked down as ground water and part of this fallen water overground/underground is returned back to ocean as run-off.This is how the water is re-circulated from ocean/land to sky and back again using solar energy.A drop of water spends 3000 years in ocean before moving to the next phase of water cycle but a drop of water spends only 8 days in atmosphere before falling down as rain.Forests help water cycle by first transpiration of water as vapor to form the clouds and then, harvesting rainfall underground to feed rivers/lakes.Satellites can measure evaporation of water from land to sky and extrapolate water consumption of a region which is useful in agriculture,forest conservation and fish farms.
Every year 502800 ckm of water evaporates from ocean to atmosphere, out of which 458000 ckm is returned back to ocean as rainfall and remaining 44800 ckm of water falls on land.Every year 74200 ckm of water evaporates from land-water to atmosphere which is returned back to land along with 44800 ckm of evaporated ocean-water totaling as 119000 ckm of rainfall on land, out of which 44800 ckm of water is returned back to ocean as run-off completing water cycle.Annual water cycle circulates 577000 ckm of water.
Table-1: how much water is needed to produce following items
Item———water in liters
1 kg beef—-16000
1 kg wheat—1350
1 kg rice—-3000
1 cup coffee-140
1 cup tea—-40
1 egg——–136
1 apple——70
1 potato—–25
1 bread slice-42
1 liter beer-155
1 liter milk–1000
leather shoes-7987
People can see that vegetarian diet consumes less fresh water than meat eating.
The water foot print of a country is the volume of water required to produce goods and services to be consumed by the people of that country.The internal water foot print is the volume of water used from domestic water sources.The external water foot print is the volume of water used in other countries to produce goods and services imported and consumed by the people of that country.The total water foot print is sum of external plus internal water foot print of a country.The average water foot print of world is 1240 cubic meters of water per capita per year.
Table-2
Country–water foot print in cubic meters per capita per year
America-2480
Britain-1695
Japan—1150
India—980
China—700
Water import dependence is the ratio of external water foot print to total water foot print of a country.Higher the ratio,more a country is dependent on outside water sources.
Table-3
Country—–water dependence ratio(percentage)
Netherlands-82
Britain—–70
Japan——-64
Brazil——8
China——-7
India——-2
People can see table-2 and table-3 and realize that countries with higher water foot prints per capita are more dependent on outside water sources than countries with lesser water foot print.
Table-4: total renewable fresh water supply in liters per capita per day by country.
country–liters per capita per day
Brazil—117602
Russia—86906
America–27388
Bangladesh-20455
China—-5820
India—-4475
People can see that more populous countries like India/China have water scarcity as compared to less populous countries.
Table-5:water consumption by energy type
Energy–water consumed in liters per megawatt-hour
solar—0.1
wind—0.1
natural gas-1000
coal—2000
nuclear power-2500
oil—-4000
hydropower-68000
biofuel(alcohol)-178000
People can see that solar/wind energy saves water.
Droughts and Floods:
Excessive rainfall is more than 20 % above normal rainfall.
Deficient rainfall is more than 20 % below normal rainfall.
Normal rainfall is up to 19 % above or below normal average rainfall.
Drought is defined as deficiency in fresh water supply for months/years due to lack of rainfall.Human activities which can worsen drought are over-farming,excessive agriculture,deforestation and soil erosion.Drought leads to adverse impact on economy,environment,agriculture,health and social factors.
Flood is defined as complete/partial inundation of normally dry areas of land by overflow of water due to any cause.It could be due to heavy rainfall,cyclones,hurricanes,broken dam,breach in the levee of a river, tsunamis etc.Besides destructive potential of flood,it can have beneficial effects in the form of recharging ground water and making soil more fertile.
SOLUTIONS TO WATER SCARCITY ARE WATER CONSERVATION AND DESALINATION.
Water conservation: Cherrapunji in India is a classical example of the need for rain water harvesting because despite annual rainfall of 11000 mm,it has water shortage for its population.Due to population growth,rapid industrialisation and expanding agriculture,the water demand has increased tremendously and to meet it,water conservation in the form of building of dams/reservoirs,digging of wells and ground water enrichment by rain water harvesting are the need of the day.In urban areas, the rainwater is collected on the roof-top of buildings and used or stored in tanks or run-off over aquifers/trees/lawns.Conservation of water in agriculture sector is a must because 75 % of fresh water is consumed by agriculture.Cultivation of salt resistant crops can use sea water and save fresh water.
What can common people do to save fresh water?
1) Discuss and encourage ways to save water with family/friends/neighbors
2) Close taps well after use.
3) Ensure that plumbing is leak proof.
4) While brushing teeth, do not leave the tap open continuously.
5) Wash your car with a bucket of water and not hosepipe.
6) Do not throw away the water used to wash vegetables/cereals but pour it on plants/trees.
7) At the time of taking hot water bath using water heater,an average household wastes 165 liters of water every day by letting water run down the drain until it is hot enough to use.Avoid such practice.
Desalination is a process by which excess salt/minerals are removed from sea water to make it potable for human consumption(fresh water). Since 97.5 % water on earth is sea water,the only other way to increase fresh water supply is desalination.
Various processes of desalination include distillation,reverse osmosis,electrodialysis,freezing and ion exchange.
Distillation is a process in which sea water is evaporated into vapor by heat leaving behind salt in a container and then, vapor is condensed to form fresh water in another container.Reverse osmosis is a process in which sea water is forced to pass through a semi-permeable membrane which only allows water molecules to pass through and salt is blocked.
Electrodialysis,freezing and ion exchange are impracticable as they need lot of energy.
Desalination plant making 200 million liters of fresh water every day needs 33 MW of electricity. Desalination is economically viable for the population near sea shore but not feasible for population far away from sea because water transport cost is high.It costs 1 dollar by distillation and half dollar by reverse osmosis for production of 1000 liters of fresh water in desalination plant which also produces 2.5 kg of carbon dioxide as a pollutant.Technological advances have made it possible to harness solar energy for desalination.
THE MORAL OF THE STORY :
1) Total amount of water on earth is same for thousands of years and will remain same indefinitely.
2) Had the fresh water been evenly distributed on earth and had there been good water management; there would be no water scarcity despite inadequate rainfall.
3) Water scarcity is defined as fresh water availability less than 1700 cubic meters per capita per year.
4) It would be stupid to wait for good monsoon every year for fresh water supply in 21’st century.
5) Population control,water conservation and desalination are the key to relieve water scarcity.
6) Vegetarian food and use of solar/wind energy saves fresh water.
Dr.Rajiv Desai.MD.