1 Water Resource: Distribution, Use Pattern and Scarcity

Objectives

The main objectives are to describe global distribution of water as oceans and seas, freshwater – surface and ground, the terminology used for ground water, water cycle, water resources scenario in India, water availability, use pattern and scarcity, water scarcity and related problems, and conclusions.

Keywords

Global distribution of water, freshwater, surface water, ground water, use pattern, water cycle, water scarcity, saline water, icecaps

 Introduction

Water is the liquid state of the hydrogen-oxygen compound H2O. Until the latter half of 18th century, scientists believed that water is a basic element characterizing all liquid substances. In 1981, the British chemist Henry Cavendish reached to the conclusion that water is a mixture of hydrogen and air. Latter on the French chemist Antoine Laurent proved that water is a compound of oxygen and hydrogen. In 1804, the French chemist Joseph Louis Gay-Lussac and the German Naturalist Alexander von Humboldt demonstrated that water consisted of two volumes of hydrogen and one of oxygen. Now the present formula of water is H2O.

Water constitutes a major portion in living matter as it obtains from 50 % to 90 % of the weight of living organism. Such as Protoplasm, the basic material of living cells consists of a solution in water of fats, carbohydrates, proteins, salts, and similar chemicals. Water is a major solvent transporting, combining, and chemically breaking down these substances. Water serves to transport food and remove waste material. A large part of animal and plant body is consisted by water. Water is also an important substance to breakdown metabolic of essential molecules such as proteins and carbohydrates. The process is called hydrolysis, which goes on continually in living cells.

Water is a vital resource to humans and is one of the life supporting layers. It has multiple uses such as in food preparation, drinking, bathing, washing, for plant and animal survival and irrigation. In addition, its large amount is used daily in industrial processes. However, water is a limited resource and the global supply of freshwater is unevenly distributed. It is abundant in some areas and scarce in other areas. Chronic water shortages exist in most of Africa and drought is common over much of the globe. Groundwater (water located blow the soil surface), reservoirs, and rivers, which are the major freshwater sources, are under severe and increasing environmental stress because of overuse, water pollution, and ecosystem degradation. In developing countries, urban sewage (over 95%) is discharged untreated into surface water – rivers and harbors (UNDP 2006).

Rain is the most ultimate and direct source of all natural potable water on the earth. However, its distribution pattern is uneven throughout the globe and thus it is resulted in under and over rainfall areas. Most of the rain runs off into streams in the case of heavy rain, or soaks into the ground, percolating through porous strata and forming ground water. Water supply system is made through reservoir in watershed areas, dams and pumps. In this module, we have described the global distribution of water as oceans and seas, freshwater – surface and ground, the terminology used for ground water, water cycle, water resources scenario in India, water availability, use pattern and scarcity, the factors affecting water scarcity and related problems, and conclusions.

Global Water Distribution

The Earth has abundant water as 71% of total areas of the Earth are covered by water. However, it distribution is extremely uneven on the Earth’s surface. Out of the total water cover, over 97% is oceanic water, which has high salinity and cannot be used. Only 2.5% of water on the surface is fresh of which, 69% resides in glaciers, 30% underground, and less than 1% is located in lakes, rivers and swamps. It means that only one 1% of the water on Earth’s surface is usable by humans and 99% of the usable quantity is situated underground and in glaciers (Table 1; Figure 1).

Table 1: Estimated Global Water Distribution

Source: Igor Shiklomanov’s 1993

    Figure 1 (A & B): Global distribution of water

In this section, a detailed description on global water distribution is given in the following paragraphs:

Oceans and Seas

About 71% of Earth’s area has water bodies, of which oceans, seas, and bays constitute about 1,333,000,000 cubic kilometers water volume, which is nearly 97.5% of total water on Earth. This huge amount of water has high salinity and is not usable for any purposes. There are total five oceans – Pacific, Indian, Atlantic (North & South), Arctic and Antarctic and they are spread mainly in the southern hemisphere. Besides, a number of seas and bays form the major water bodies worldwide. Ocean water is saline and it cannot be used for any human activities. Over the oceans, evaporation is greater than precipitation, so the net effect is a transfer of water back to the atmosphere. In this way, freshwater resources are continually renewed by counterbalancing differences between evaporation and precipitation on land and at sea, and the transport of water vapor in the atmosphere from the sea to the land.

Freshwater

   Freshwater accounts for only some 2.5% of the world’s water supply, which includes 68.7% glaciers, 30.1% groundwater, and permafrost 0.8%. Freshwater lakes account 67.4%, wetlands 8.6%, soil moisture 12.2%, rivers 1.6%, atmosphere 9.5%, and plants and animals 0.8%. Although, possesses very less amount of water yet, it is essential for human uses such as drinking, agriculture, manufacturing, and sanitation. Freshwater is found as surface and groundwater. In many areas, freshwater contains a large amount of salinity however, in other areas; supplies of freshwater (surface) exist because precipitation is greater than evaporation on land.

Surface water Resources

Surface water includes rivers, lakes or fresh water wetlands. Precipitation is the natural recharging sources for the surface water and it also maintains the hydrological cycle. Human activities like artificial dams, reservoirs are also included in the same category and have capacity to increase utilization of the water.

Ice sheets and glaciers are not always thought of as freshwater sources, but they account for a significant fraction of world reserves. Nearly 90% of the water in icecaps and glaciers is in Antarctica, with another 10% in the Greenland ice sheet and the remainder in tropical and temperate glaciers. Rivers occupy a relatively small share of fresh water, but they are the large part of the global hydrologic cycle and are centrally important in shaping landscapes. A large amount of freshwater flow passes through several of the world’s largest rivers: the Amazon carries 15% of total river flow on Earth, the Congo carries 3.5%, and rivers that flow into the Arctic Ocean carry 8%. In India, the Ganges, Sind and Brahmaputra and in China, Huang Ho is the major river systems, which provide fresh water to more than 50% of the populations. Similarly, there are a number of river systems worldwide, which provide freshwater to human activities.

Groundwater Resources

Most of the precipitation that is not transpired by plants or evaporated, infiltrates through soils and becomes groundwater, which flows through rocks and sediments and discharges into rivers. Further, rainwater infiltrates though pores to underground. Rivers are primarily supplied by groundwater, and in turn provide most of the freshwater discharge to the sea. Water sources like subsurface water or water within aquifers are known as groundwater resources. About 30.1% of global freshwater is found as underground.

Groundwater is the second largest available reservoir of freshwater. Out of the world’s freshwater, the majority is locked away as ice in the polar ice caps, continental ice sheets and glaciers. Surface waters such as rivers and lakes only accounts for less that 1% of the worlds freshwater reserves whereas groundwater accounts for 30.1% of the worlds freshwater resources. Millions of people worldwide depend on groundwater stocks, which they draw from aquifers – permeable geologic formations through which water flows easily.

Major Terminology used for Groundwater

Porosity

The proportion of total volume that is occupied by voids, like the spaces within a pile of marbles. Porosity tends to be larger in well-sorted sediments where the grain sizes are uniform, and smaller in mixed soils where smaller grains fill the voids between larger grains. Soils are less porous at deeper levels because the weight of overlying soil packs grains closer together.

Permeability

Medium transmits water, based on the size and shape of its pore spaces and how interconnected its pores are called permeability. Materials with high porosity and high permeability, such as sand, gravel, sandstone, fractured rock, and basalt, produce good aquifers. Low-permeable rocks and sediments that impede groundwater flow include granite, shale, and clay. Groundwater recharge enters aquifers in areas at higher elevations (typically hill slopes) than discharge areas (typically in the bottom of valleys), so the overall movement of groundwater is downhill. However, within an aquifer, water often flows upward toward a discharge area.

Hydraulic Head

Hydrogeologists use a quantity to understand and map the complex pattern of groundwater flow is called the hydraulic head. The hydraulic head at a particular location within an aquifer is the sum of the elevation of that point and the height of the column of water that would fill a well open only at that point. Thus, the hydraulic head at a point is simply the elevation of water that rises up in a well open to the aquifer at that point.

Depending on local rainfall, land use, and geology, streams may be fed by either groundwater discharge or surface runoff and direct rainfall, or by some combination of surface and groundwater. Perennial streams and rivers are primarily supplied by groundwater, referred to as baseflow. During dry periods they are completely supplied by groundwater; during storms, there is direct runoff and groundwater discharge also increases.

Water Cycle

Water is perhaps the most important component of any ecosystem. All living organisms need water to grow and survive. In an ecosystem, water cycles through the atmosphere, soil, rivers, lakes, and oceans. Some water is stored deep in the earth called groundwater. The water moves from one reservoir to another, such as from river to ocean or from ocean to the atmosphere by the physical processes of evaporation, condensation, precipitation, infiltration, surface runoff and subsurface flow and it is called water cycle. Water cycle or hydrological cycle is an important process of the land and atmosphere, which brings rain on Earth and supports life on Earth. There are main four stages in the water cycles, which are also called components of water cycle. They are evaporation, condensation, precipitation and collection. When warmth from the sun causes water from oceans, lakes, streams, ice and soils to rise into the air and turned into water vapour (gas) is called evaporation. After reaching in the Troposphere, which is cold layer of atmosphere, the water vapour becomes cool and condensed and that leads to formation of cloud. This whole process is called condensation. Then, the water falls from the sky as rain, snow, sleet or hail is called precipitation. The water sinks into the surface also collects into lakes, oceans or aquifers. It evaporates again and continues the cycle. The fundamental characteristics of the hydrological cycle are that it has no beginning and it has no end.

Solar radiation drives evaporation by heating water so that it changes to water vapor at a faster rate. This process consumes an enormous amount of energy – nearly one-third of the incoming solar energy that reaches Earth’s surface. On land, most evaporation occurs as transpiration through plants: water is taken up through roots and evaporates through stomata in the leaves as the plant takes in CO2. A single large oak tree can transpire up to 40,000 gallons per year. Much of the water moving through the hydrologic cycle thus is involved with plant growth. Since evaporation is driven by heat, it rises and falls with seasonal temperatures. Water also evaporates though transpo-evaporation on land. The soils absorb water and when it gets heat, evaporation takes place. This process is called evapo-transpiration.

The hydrologic cycle is also coupled with material cycles because rainfall erodes and weathers rock. Weathering breaks down rocks into gravel, sand, and sediments, and is an important source of key nutrients such as calcium and sulfur. Estimates from river outflows indicate that some 17 billion tons of material are transported into the oceans each year, of which about 80% is particulate and 20% is dissolved. Figure 2 shows water the Earth water cycle.

Water Resources Scenario in India

In India, rivers are the major source of water. Here, utilizable annual surface water in rivers of the country is 690 km3. Groundwater is other major source of water, which is recharged from the precipitation mostly in the monsoon season. The annual potential of natural groundwater recharge from rainfall is about 342.43 km3, which is 8.56% of total annual rainfall of the country. Irrigation systems including canal irrigation also contribute to the recharging in the groundwater. The annual potential groundwater recharge augmentation from canal irritation system is about 89.46 km3 (Kumar et al., 2005). Water is very scarce and polluted in most of the Indian cities. Further, water supply is insufficient, low or erratic. Rural areas too are facing low quality of water. Table 2 shows average water flow and utilizable water in top fifteen river basins in India.

Table 2: Average water flow and utilizable water in top fifteen river basins in India

    A large part of India is facing water scarcity mainly during the summer season, which includes, Rajasthan, part of Madhya Pradesh, Maharashtra and Gujarat and southern states. In the meantime, its large part is inundated during the monsoon season. It means that drought and flood prevails together in India.

Water Availability Use Pattern and Scarcity

Out of the total water available globally, >97% is saline and >2% is frozen in icecaps; water in ice cap is an important source of rivers. Only less than 0.7% of total water is available for human use. The total amount of water on Earth is estimated at 385,580*10^10 gallons thus per capita share is about 9*10^10 gallons of water. Because about 97% of total water is saline, therefore freshwater supply is certainly limited (FAO 2007)

Currently, from 10,000 to 12,000 cubic kilometers of freshwater are available for human consumption each year worldwide. In the year, 2000 humans withdrew about 4,000 km3 from this supply. About half of the water withdrawn is evaporated, transpired by plants, or contaminated beyond use, and so became temporarily unavailable for other users. The other 50% was returned to use; for example, some water used for irrigation drains back into rivers or recharges groundwater, and most urban wastewater is treated and returned to service. Of the water withdrawn for human use, 65% went to agriculture, 10% to domestic use (households, municipal water systems, commercial use, and public services), 20% to industry (mostly electric power production), and 5% evaporated from reservoirs. About 70% of the water used for agriculture was consumed, compared to 14% of water used for domestic consumption and 11% of water used for industry. Both population levels and economic development are important drivers of world water use. If current patterns continue, the World Water Council estimates that total yearly withdrawals will rise to more than 5,000 km3 by 2050 as world population rises from 6.1 billion to 9.2 billion. During the 20th century, world population tripled but water use rose by a factor of six. The United Nations and the international community have set goals of halving the number of people without adequate safe drinking water and sanitation by 2015. Meeting this target will require providing an additional 260,000 people per day with clean drinking water and an additional 370,000 people per day with improved sanitation through the year 2014, even as overall world demand for water is rising.

Water scarcity can be defined as the point at which the aggregate impact of all users impinges on the supply or quality of water under prevailing institutional arrangements to the extent that demand by n all sectors, including the environment, cannot be satisfied fully. One of the main problems that face by the world’s society in the 21st century is water scarcity. In comparison to the last century, water use has been growing at more than twice the rate of population increasing. A number of regions are increasing with chronically shortage of water. Every continent is facing water scarcity. Almost one-fifth of the world’s population (around 1.2 billion people) live in areas of physical scarcity and nearly 500 million people are on the verge of water scarcity. Some countries lack the necessary infrastructure to take water from rivers and aquifers. About 1.6 million people (almost one-quarter of the world’s population) face economic water shortage (Figure 3).

Figure 3: Water scarcity regions of the world

Source: World Water Development Report 2012.

Uneven distribution of freshwater is one among the causes of water scarcity otherwise there is enough freshwater on the planet for seven million people. On the other hand, a large amount of water is wasted, polluted and unsustainably managed and thus, we can conclude that water scarcity prevails due to the factors both natural and human. Climate change has a greater impact on global water resources. As temperature increase, evaporation increases, sometimes resulting in droughts. In addition, rising temperature is melting glacial ice. Glaciers are the major sources of freshwater, are in danger of disappearing within the 21st century. Receding glaciers are the most important phenomena due to rising temperature, which is leading to water scarcity.

Climate scientists predict that there will be a profound impact of climate change on the hydrologic cycle, and that in many cases these effects will make existing water challenges worse. Rising global temperatures will alter rainfall patterns, making them stronger in some regions and weaker in others, and may make storms more frequent and severe in some areas of the world. Summing up, climate change is likely to make many of the water-management challenges that are outlined in this unit even more complex than they are today.

Worldwide, about 700 million people in 43 countries suffer from water scarcity. By 2030, almost half the world’s population will be living in the areas of high water stress including between 75 and 250 million people in Africa mainly due to climate change. This figure may increase in the Sub-Saharan Africa. Coping with water scarcity worldwide, the UN has launched awareness programme through observing world water day to combat desertification.

Expansion of agriculture, damming, diversion, over-use, and pollution threaten water resources in many parts of the globe. It is the greatest challenge to the government to provide safe drinking water for the more than 1 billion people who are suffering from water scarcity. Particularly developing countries, safe water, free of pathogens and other contaminants, is unavailable too much of the population, and water contamination remains a concern. Even, it is challenging for developed countries with good water supplies and advanced treatment systems. Over-development, especially in coastal regions and areas with strained water supplies, is leading many regions to seek water from more and more distant sources. In a city where water is also used for cleaning, manufacturing, and sanitation, per capita use is around 150 gallons per day.

Millions of people die each year of preventable water-related diseases. In 2002, 1.1 billion people around the world (17% of global population) did not have access to safe drinking water and 2.6 billion people (42% of global population) lived without adequate sanitation. Countries located in Africa, Asia, and the Pacific is suffering from inadequate supplies of safe drinking water. However, this problem also persists elsewhere. In Europe, many households lack adequate sewage treatment services. An inequity among water users is widespread: cities often receive better service than rural areas, and many poor communities in both rural and urban areas lack clean water and sanitation.

Water Scarcity and Related Problems

There are many factors affecting the prevailing water scarcity in the world’s countries. Some of them are described below.

Depleting Water Resources

Water resources both surface and groundwater are depleting an alarming rate, worldwide. The reasons are many. However, three reasons are prominent. The first one is mounting population. The freshwater is limited whereas its uses – drinking, household, irrigation and industrial – are increasing. The second reason is pollution. Water sources are polluted due to large-scale human activities and in many areas, water cannot be used for daily human activities. The third cause is climate change. Climate change has influenced the global pattern of precipitation, and in most of the areas, it is scarce. Receding glacier and ice caps due to global warming is other cause for future scarcity of water. People are extracting water from aquifers more quickly than the aquifers are replenished by recharge. In addition to draining aquifers, excessive groundwater pumping changes groundwater flow patterns around wells and can drain nearby rivers and streams.

Water Salinization

Water salinity is also increasing in many parts of the world due to influence of several factors. Among them, the main factors are prolonged drought, less rainfall and excessive use of surface water. When freshwater resources become saline, they can no longer be used for irrigation or drinking. Saline water is toxic to plants, and high sodium levels cause dry soils to become hard and compact and reduce their ability to absorb water. Irrigation water becomes toxic to most plants at concentrations above 1,300 milligrams/liter; for comparison, the salinity of seawater is about 35,000 mg/l.

Water Pollution

Different types of contaminants can pollute water and render it unusable. Pollutants primary drinking water standards include:

Microorganisms such as cryptosporidium, giardia, and fecal coliform bacteria

Disinfectants and water disinfection byproducts including chlorine, bromate, and chlorite

Inorganic chemicals such as arsenic, cadmium, lead, and mercury Organic chemicals such as benzene, dioxin, and vinyl chloride

    Radionuclides including uranium and radium

Surface water – rivers, lakes and wells are highly polluted mainly in the developing countries and their water is not usable which leads to further scarcity of water. Development in all sectors and establishment of industries are the major causes of water pollution.

Water-Borne Diseases

More than two million people die each year from diseases such as cholera, typhoid, and dysentery that are spread by contaminated water or by a lack of water for hygiene. Cholera, typhoid, and dysentery, are caused by drinking water containing infectious viruses or bacteria, which often come from human or animal waste. Skin and eye infections, are caused by lack of clean water for washing. The developing countries are facing this problem largely.

Conclusion

Water is a precious resource, a life giver substance however, it is scarce. As oceanic water covers above 97% of total water volume and it is saline, it cannot be used for any human activities. A large volume of freshwater is located as ice cape an in Antarctica and Arctic, which is also unused. Further, overuse and high pollution in freshwater resource create acute water scarcity worldwide. As a result, many countries of the world are facing acute shortage of water. If this situation is continued further, it will have devastating consequences. Therefore, conservation of water for larger interest of humanities is inevitable.

References

• FAO (2007) Coping with water scarcity, Challenge of the twenty-first century UN-Water Igor Shiklomanov’s (1993) ‘World fresh water resources’ in Peter H. Gleick (Ed.), Water in Crises: A Guide to the World Fresh Water Resources, Oxford University Press, New York.
• Kumar, R, Singh, R. D. and Sharma, K. D. (2205) Water resources of India, Current Science, Vol. 89, No. 5, 10 September 2005 UNDP (2006). Human Development Report 2006 World Water Development Report (2012) World Water Assessment Programme, March 2012.
• John McPhee, “Atchafalaya,” in The Control of Nature (New York: Farrar Strauss Giroux, 1989). A renowned journalist describes the technical challenges and environmental impacts of human efforts to manage the flow of the Mississippi River.
• Peter H. Gleick, The World’s Water 2006–2007: The Biennial Report on Freshwater Resources (Washington, DC: Island Press, 2006). Current information on water needs, trends, and policies worldwide.
• Sandra Postel, Liquid Assets: The Critical Need to Safeguard Freshwater Ecosystems, Worldwatch Paper 170 (Washington, DC: Worldwatch Institute, July 2005). An overview of the valuable functions performed by freshwater ecosystems and policy options for protecting them.