Founder : Len Abrams
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The following is an excerpt from River Keepers Handbook: A Guide to Protecting Rivers and Catchments in Southern Africa, a new report by IRN (International Rivers Network). This section describes some of the many alternatives to water supply which can help human society flourish without undermining the integrity of the ecological systems we depend on. More information.
by Lori Pottinger
New Approaches to Water Supply
Using water more efficiently can in effect create a new source of supply. According to Sandra Postel, an expert in international water scarcity problems, technologies and methods are now available which could cut water demand between 40-90 percent in industry, 30 percent or more in cities, and between 10-50 percent in agriculture without reducing economic output or quality of life. In developing countries, the potential benefits of water demand-side management programs are huge in terms of money saved and ecological damage avoided, as well as freeing up water supply to extend coverage to the unserved.
Demand management includes several approaches to conserve water, including economic policies, notably water pricing; laws and regulations, such as restrictions on certain types of water use; public and community participation, to ensure that solutions are workable and have public support, and technical solutions, such as installing water flow restrictors. Reducing the amount of water consumed is key to cutting water expenses. Demand management cannot be thought of only from a technical angle. Water-saving technical measures always have economic, legal, institutional and political aspects that must be considered as well.
Modified Agricultural Practices
Since agriculture accounts for nearly 70 percent of the world's fresh water withdrawn from rivers, lakes, and underground aquifers for human use, the greatest potential for conservation lies with increasing irrigation efficiency. By reducing irrigation by 10 percent, we could double the amount available for domestic water worldwide. This can be done by converting to water-conserving irrigation systems; taking the poorest and steepest lands out of production; switching to less-thirsty crops (which may require changes to government subsidies for certain crops); implementing proper agricultural land drainage and soil management practices, and reducing fertilizer and pesticide use.
Typically, governments provide water to large commercial farmers at greatly subsidized rates, decreasing the need for conservation and promoting wasteful practices. Studies show that just 35-50 percent of water withdrawn for irrigated agriculture actually reaches the crops. Most soaks into the ground through unlined canals, leaks out of pipes, or evaporates before reaching the fields. Although some of the water lost in inefficient irrigation systems returns to streams or aquifers, where it can be tapped again, water quality is invariably degraded by pesticides, fertilizers and salts that run off the land. This is in fact another way that commercial agriculture "uses" water: by polluting it so that it is no longer safe to drink.
Switching to conserving irrigation systems has the biggest potential to save water. Experts say drip irrigation could potentially save 40-60 percent of water now used for agriculture. Conventional sprinklers spray water over crops, not only irrigating more land than is needed but also losing much to evaporation. Drip irrigation, however, supplies water directly to the crop's root system in small doses, where it can be used by the plant's roots. This keeps evaporation losses low, at an efficiency rate of 95 percent.
Although by 1991 some 1.6 million hectares were using drip irrigation worldwide, this is still less than one percent of all irrigated land worldwide. Some countries have made drip irrigation a serious national priority, such as Israel, which uses drip irrigation on 50 percent of its total irrigated area. But clearly it is the exception, and most dry countries have a long way to go.
Another conserving practice is to reuse urban wastewater on nearby farms. Today, at least half a million hectares in 15 countries are being irrigated with treated urban wastewater, often referred to as "brown water." Israel has the most ambitious brown-water program of any country. Most of Israel's sewage is purified and reused to irrigate 20,000 hectares of farm land. One-third of the vegetables grown in Asmara, Eritrea, are irrigated with treated urban wastewater. In Lusaka, Zambia, one of the city's biggest informal settlements irrigates its vegetable crops with sewage water from nearby settling ponds.
New Sources for Water
Although demand-management should always be examined first when additional water is needed, conservation will not always preclude the need for new sources of supply. There are many sustainable ways to get water which cause less damage to ecosystems and communities than the large-scale infrastructure projects currently in favor with planners.
Rainwater Harvesting: Around the world, more communities are returning to small-scale water harvesting, usually using a system that collects water from house rooftops. A South African group, Association for Water and Rural Development (AWARD), teaches people how to collect water from the roof of a house, school or other building. The group calculates that for every 30mm of rain falling, a house with a 50m2 roof designed to funnel it into a water tank could collect 1200 liters. AWARD estimates that this could save a person 16 trips to the local water-collection source.
Desalination: Some 70 percent of the earth's surface is water, but most of that is undrinkable seawater. By volume, only 3 percent of all water on earth is fresh water, and only about 1 percent is easily accessible surface freshwater. Water desalination is a process used to remove salt and other dissolved solids to create fresh water.
Desalination is an attractive water source for many reasons, especially because the supply is virtually limitless and unaffected by drought. For coastal countries, desalted water is not vulnerable to political changes, unlike water supply from shared rivers. Desalting technologies can be built in stages to meet demand, unlike most large-scale water infrastructure projects. Desalination projects also do not lead to the displacement of indigenous peoples, changed agricultural lifestyles or serious ecological impacts.
In most cases, desalted water is not the sole source of a community's water supply (though this may change as the cost of desalted water goes down); it is usually combined with water from less expensive sources. In 1991, desalting plants in approximately 120 countries worldwide had the capacity to produce 4.1 billion gallons a day.
The most common concerns about desalination are that the process is too expensive and consumes too much energy. In some places, desalinized water costs many times more than conventional local water sources. However, technical breakthroughs are beginning to lower the price (although still not to the artificially low levels that agribusiness is used to paying for water). Cost comparisons for desalted water are often made to existing water supplies, which generally did not include a full, fair cost-benefit analysis when they were developed. To be fair, comparisons should be made to the cost of developing other new sources (including environmental and social costs in the analysis).
The amount of salt to be removed greatly affects the cost of desalting, as does the method used to remove salts. The most significant factor in desalinated water is energy. Energy for most current technologies amounts to about 30-40 percent of the total cost.
There have also been recent breakthroughs that are expected to reduce the costs for desalination, primarily by cutting back how much energy is required. For example, in 1998 the Singapore-based company AquaGen International announced that it has developed a cheaper, portable water desalination plant that can be assembled anywhere quickly. AquaGen says the modular system of its plant makes installation easy. The unit can produce 100 cubic meters (25,000 gallons) of water for less than US$300,000. The company says that its plants are up to three times more energy efficient than those now in use. The plants are relatively small, producing up to 5,000 cubic meters of drinking water per day (compared to up to 327,000 cubic meters/day for the big plants in the Middle East). AquaGen is doing a feasibility study for a plant that can process 45,000 cubic meters and hoped would be operational in four years.
Israeli, Palestinian and US scientists are embarking on an ambitious desalination program that is intended to create a "New Desalinized Middle East." One of the program's goals is to build solar-powered desalination machines that can fit on a truck, then teach villagers to use them and even make them. The program will also look at how water is affected by salt and pollutants. The fully self-supporting desalination system was being evaluated in early 1999 by Al-Azhar University in Gaza, Palestine. The system can desalinate up to 600 liters of brackish water a day. It is being designed with irrigation in mind, and the plan is to develop micro-irrigation systems in parallel. The units require little maintenance, as they have few moving parts.
New developments in alternative energy may prove to be a boost for desalination as well. Solar thermal power and fuel cells may provide good sources of power for desalination plants. Since places with good solar power potential are usually the places most in need of water, there is a huge potential to link the two.
Recycling Waste Water: A largely untapped source of water for irrigation and groundwater recharge is treated municipal wastewater. Recycling this "waste" product into a reliable water supply has huge benefits. It makes use of the nutrients in sewage to feed crops and keeps them from polluting waterways. It postpones the need to enlarge and update costly new sewage discharge systems, and eliminates the problems from discharging wastewater into rivers and oceans. It protects freshwater ecosystems by reducing the amount of water extracted from rivers and lakes. Recycled wastewater can also be used to help restore aquatic ecosystems harmed from over-extraction. Using recycled wastewater instead of importing water from hundreds of kilometers away can also result in significant energy savings.
Israel has the most advanced system of waste water recycling. Currently, 70 percent of sewage is treated and used for irrigation. Officials predict that by 2010, one-fifth of the nation's total water supply will come from recycled waste water. Israel uses many different treatment schemes for its many water-reuse projects. One method relies on algae-activated organisms to treat the waste water. The waste water is initially stored in a series of ponds in which the anaerobic and aerobic treatment is sufficient to irrigate crops.
Calcutta, India, channels much of its raw sewage into a system of natural lagoons, where fish are raised. The city's 3,000 hectares of lagoons produce about 6,000 metric tons of fish a year for urban consumers. The fish are safe to eat because the complex biological interactions in the lagoons remove harmful pathogens from the sewage.
As the technology to treat wastewater has improved, so have the applications for the use of the water. A small but growing number of cities are beginning to use highly treated wastewater to supplement drinking water supplies. Windhoek, Namibia, for example, was the first city in southern Africa to used recycled waste water in its public supply and has been doing so for more than 15 years.
Highly treated wastewater cannot be piped directly into a water supply. Most commonly, wastewater is used to augment the drinking-water supply by adding it first to a lake, reservoir, or underground aquifer. The mixture of natural and reclaimed water is then subjected to normal water treatment before it is distributed as drinking water for the community.
There is also much water to be gained by reducing that used for sewage treatment. Treating waste is a hugely water-intensive process, and the commonly used systems cannot be sustainably expanded to serve the three billion people now without access to sewage treatment. Natural water treatment systems such as using wetlands often can be an alternative to modern water treatment technologies. Recycling waste for agricultural purposes by using oxidation ponds and aerated lagoons does not require as much land as is often assumed; however, the land requirement of oxidation ponds is a stumbling block for their use – particularly in urban areas. Moreover, it decreases pollution, reduces the need for fertilizers, and often can be accomplished with small-scale, low-cost technology that is based on local traditions, is decentralized and ecologically sound.
or in South Africa (for
2000/1 Water Policy International Ltd -