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5. How can the growing demand for water be met?

  • 5.1 Intercepting, diverting, storing and transferring water
  • 5.2 Water re-use
  • 5.3 Desalination

The response to the growing demand for water has focused on compensating for natural variability and improving the quality and quantity available.

In dry regions, new ways to meet demand—such as desalination, re-use, replenishment of underground water, and transfer between river basins – are complementing conservation methods that have been in use for a long time.

In regions where water is more abundant it was often assumed that shortages could be overcome and that pollution or damage to ecosystems could be undone. It was not generally expected that human activities would deplete water resources and endanger ecosystems as much as they have. Consequently, some of the same practices used in dry regions are now being adopted in those with sufficient water.

Awareness of the relationship between water resources and ecosystem health has increased recently, and there has been a growing focus on how the condition in a river, wetland or coastal zone supports economic development and poverty alleviation. More...

5.1 Intercepting, diverting, storing and transferring water

5.1.1 People have been collecting rainwater for thousands of years – for example in Palestine, Greece, Rome, and South Asia. In India, rainwater has recently been used to replenish underground water. This technique is inexpensive and can be implemented locally. Larger projects have also been carried out to increase infiltration into the ground in areas where deforestation has reduced the availability of water. More...

5.1.2 Diverting surface water into basins and pits to increase infiltration into the ground can reduce evaporation, help replenish groundwater aquifers, and improve the quality of water. This practice is used in the Middle East and the Mediterranean. Runoff is collected and diverted in a variety of ways. Some methods reduce the need to treat the water.

For example, in Binh Thuan province in Viet Nam, a large area of tropical forest was cleared to make room for rice fields. This led to desertification and severe water shortages in periods of low rainfall. To remedy the situation, rainfall is being diverted into aquifers during the rainy season for use during the dry season. The quality of underground water has improved, and it can be used for a variety of purposes, including farming.

A number of associations are working with UNESCO and international donors to support these techniques by conducting research, building local capacity, and running pilot projects in Australia, China, Europe, Kenya, Mexico, Oman, South Asia, Southern Africa, and the United States. More...

5.1.3 Dams and reservoirs provide hydropower, supply water during shortages, enable fishing and the irrigation of farmland, and protect people from both floods and droughts.

However, they have also had a significant negative impact, including on the water cycle, and have brought about social and environmental consequences. In response to media attention and protests, fewer large dams are being built for the moment and alternatives are being considered. Some dams have been decommissioned, or modified to allow releases of water. Keeping a balance between the water that enters a reservoir and the water that is released yields significant benefits. More...

5.1.4 The long-standing practice of interbasin transfer of water from one aquifer or river basin to another can help alleviate water shortages caused by agriculture and other human activities. In India, a long-distance link is being proposed between rivers to counteract droughts and floods. There are major interbasin links existing in China, and more are under consideration or being planned for instance between the basins of the Yangtze and Yellow River. Though such schemes may be technically feasible, their impact on people and the environment must be considered before they are implemented. More...

5.2 Water re-use

The re-use of wastewater, made possible by technological advances in the last century, is now widespread. Once it has been extensively treated to remove biodegradable material, nutrients, and pathogens, it could be drunk, or used in a number of other ways. Non-potable quality water can be used directly for irrigation, as a coolant in industry and to maintain river flows. Cities around the world where freshwater supplies are limited, such as San Diego in the United States, are developing programmes to re-use water and to replenish aquifers with treated wastewater. Use of these techniques is expected to increase. The most viable programmes use reclaimed waste water instead of drinking water for agricultural, industrial, and other uses.

Countries in both water-short and more temperate but high-population regions are expected to increase their use of reclaimed water in the coming years. Reclaimed water is expected to account for 25% of Israel’s water supply in the next few years. Jordan will have to increase its use of reclaimed water fourfold to meet demand; Egypt, tenfold. Most Middle Eastern countries are expected to re-use more than half their wastewater.

Australia, Belgium, China, Germany, Japan, and the United Kingdom are also expected to increase their use of reclaimed water, as this practice becomes an integral part of the management of water resources. More...

5.3 Desalination

Desalination involves reducing its mineral content by taking salt out of seawater and brackish water and producing water of freshwater quality. It is used mainly by cities and industry, primarily in the Middle East (50%), but also in North America (16%), Europe (13%), and Asia (11%). The high costs of desalination, principally arising from the energy used, have dropped significantly in recent years due to technological advances.

That energy is produced primarily with fossil fuels, which pollute the air, and each method of disposing of the by-products of desalination—for example in the ocean or in deep wells—has an impact on the environment. It has been suggested that the various means of disposal be assessed according to a single set of criteria, so that the impact of each desalination plant can be consistently evaluated.

It is expected that desalinated water will be put to new and innovative uses, particularly to support a variety of economic activities in coastal areas. More...