Water Resources Management and Conservation
Human demand for water has been growing for two reasons. Firstly, it is primarily because of the growth of the human population. Secondly, as the human standards of living improve in the various countries of the world, the demand for water also increases to meet new needs in industry, agriculture and domestic use. However, there is a limited quantity of fresh water on Earth and for many nations this resource is scarce in its availability. People in Canada and the United States, for example, believe that clean water is available to them in an unlimited supply. Nevertheless, supplies are not unlimited but finite and increasing demand for this resource will soon create problems that can only be corrected by management and conservation. People are also beginning to recognize that water is important for things other than domestic, agricultural and industrial purposes. Water is important for maintaining fish and wildlife populations, for recreation and for aesthetics. Governments in many countries have now established water resource management programmes that aim to provide a sustainable supply of high quality water in an efficient and environmentally sound manner.
Water Conservation Techniques
A number of techniques and technologies can be used to make agricultural, industrial and domestic water use more efficient. Reductions can easily occur in the following areas:
Reducing Agricultural Waste: Irrigation accounts for 70 per cent of the world's water use. Most irrigation systems deliver water to crops by flooding the land surface, diverting water to fields via open channels, or by sprinkler systems that apply water to the field surface. In general, these methods are very inefficient as only 50 per cent of the water applied is absorbed by the plants. The rest is lost to the atmosphere by evaporation. Micro-irrigation techniques can reduce the amount of water applied to crops by 40 to 60 per cent. Other strategies that can be used to reduce agricultural water use include:
= The cultivation of food crops that require less water for growth.
= The use of lined or covered irrigation canals to reduce infiltration and evaporation losses.
= Irrigating crops at night or early morning when evaporation potentials are low.
= Reduce water subsidies and encourage the proper pricing of this resource.
Reducing Industrial Waste: Industry is the second largest user of water supplies. Reducing the amount of water used in industry not only makes more water available for other purposes but it can also reduce the volume of pollution. Industry reductions can be achieved by:
Designing industrial processes to recycle water: For example, water used for industrial cooling purposes can be cooled down in a cooling tower and then reused.
= Increasing the cost of water to industries to encourage water recycling.
= Recycling materials themselves can also greatly reduce water demand. For example, manufacturing a ton of aluminum from scrap rather than from virgin ore can reduce the volume of water used by 97 per cent.
= Reducing Domestic Waste - Some strategies for reducing domestic consumption include:
= Replace lawns in semiarid and arid urban areas with xeriscaped surfaces.
= Encourage the use of efficient irrigation systems for home garden and lawn use.
= Manufacture and legislate the use of more efficient dishwashers, washing machines, and bathroom showers and toilets.
= Encourage leak detection and repair for distribution systems. Distribution systems in many of the world's urban areas are losing between 25 and 50 per cent of their water supplies due to leaks in pipes.
= Properly price water for domestic use. This price must reflect the environmental cost of over consumption and resource degradation. Many studies have shown that higher prices for water provide motivation for people to conserve. The introduction of water meters in Boulder, Colorado reduced water use by about 30 %. In Canada, water is metered in approximately two-thirds of the municipalities.
= Education can encourage people to reduce the amount of personal consumption.
Increasing Water Supplies
Humans have used several different methods to increase supplies of water. Some of these techniques involve the modification of the runoff process. Dams and reservoirs have been used for many centuries to trap runoff behind earth or concrete walls. The stored water is then transferred via canals or aqueducts for use in agriculture, industry, or domestic processes. Worldwide there are now over 36,000 operational dams, some of which are also used to generate energy.
Several problems can occur with the storage of water in these human created features. In some reservoirs, sediments can accumulate to a point where they can no longer be used for water storage or hydroelectric production. Other reservoirs have severe evaporation or leakage problems. Large amounts of water are annually lost from the Aswan High Dam in Egypt because of evaporation. This problem has reduced the planned amount of irrigation water supplied by this dam by one-half.
In recent years, many nations have increased their supply of freshwater by exploiting the water found beneath the Earth's surface. Groundwater contains more than 10 per cent of the freshwater found in the hydrosphere. Saudi Arabia receives 75 per cent of its water supply from groundwater mining. In many cases, withdrawal rates of this water greatly exceed the natural rates of recharge. Depleting groundwater reservoirs can lead to a number of problems, including: subsidence, earthquakes, sinkhole development, and saltwater intrusion.
Many projects have used canals, aqueducts, and diversion techniques to move water to places of need. In the former Soviet Union, diversions on the Amu Dar'ya and Syr Dar'ya Rivers have been used to create irrigation water for cropland. However, these diversions are also responsible for reducing the flow of runoff water to the Aral Sea. Because of the reduced flow, the Aral Sea has declined in area by over 50 %, has lost two-thirds of its volume, and has greatly increased in salinity. At current rates of reduction, the Aral Sea could be gone by 2020.