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World Resources 1996-97 (A joint publication by The World Resource Institute, The United Nations Environment Programme, The United Nations Development Programme, and the World Bank) (Edited by Dr. Róbinson Rojas)
5. Urban Priorities for Action
Promoting Water Conservation
For most cities, extending water supply coverage to current residents is challenge enough. Yet cities are also facing pressures to expand their municipal water supplies; demand for municipal water could grow by a factor of five or more over the next four decades (36). Many cities already face critical water shortages and high costs of supply.
The usual response is to increase supplies through expensive investments in new public infrastructure. Yet evidence suggests that cities can also manage the demand for water by reducing wasteful use (through pricing and conservation efforts) and by preventing pollution. A comprehensive strategy would include improving the operation and maintenance of water supply systems, removing subsidies and price distortions that encourage waste, and public education (37). Demand management is a particularly attractive option for cities in the developed world, where per capita water consumption is many times that in the developing world. Recycling, especially of industrial wastewater, is another attractive strategy, providing companies with a cost-effective and reliable source of water and at the same time protecting the environment (38).
In Boston, impending costs of supplying water to the city led officials to implement a Long Range Water Supply Program (LRWSP) to cut down on water use. Between 1988 and 1993, LRWSP reduced the average daily demand for water from 1.2 million to 0.9 million cubic meters (39). The program focused on detecting and repairing leaks, metering, retrofitting showerheads and toilets with more efficient technologies, protecting water sources from pollution, and building support for the program among city residents through outreach and education. These reductions eliminated the need to develop new supplies--saving hundreds of millions of dollars--and the water system is operating within its safe yield for the first time in 20 years (40).
In developing countries, several cities have been implementing demand management programs. In Mexico City, for instance, the water utility implemented a new rate structure that charges more per cubic meter as consumption levels increase. It is hoped that this measure will provide metered industries with incentive to conserve water (41). In Sao Paulo, Brazil, the imposition of effluent charges induced reductions in water demand between 42 and 62 percent at three industrial plants (42).
A study in Beijing showed that a combination of strategies could reduce industrial water consumption by about one third, at a cost substantially less than that of investing in new supplies. The measures included increased recycling of cooling water in manufacturing; recycling of cooling water in power plants; and wastewater recycling. Similarly, about 15 percent of domestic consumption could be saved through measures such as improved efficiency in public facilities, a leakage reduction program, recycling of cooling water used in air conditioning, and installation of water-efficient flush toilets (43).
Reducing Water Pollution
By reducing water pollution, cities can reap the double benefit of effectively increasing the water supply while lessening the deterioration of the aquatic environment. As the "pollution shadow" spreads, cities must go further afield to find clean water, which significantly increases the costs of water supply. Shanghai, China, for instance, moved its water intakes 40 kilometers upstream at a cost of $300 million because of the degradation of river water quality around the city (44) (45).
Of all the pollutants, urban sewage may be the worst offender in near-urban waters, although industrial pollutants can be a major source. In addition, up to half of the contaminants reaching urban waters come from nonpoint sources, such as urban runoff. Controlling urban runoff, although difficult, is essential if cities are to mitigate their impacts on nearby water bodies.
Preventing pollution in the first place may be the best long-term solution. One study in Santiago, Chile, found that although full wastewater treatment would cost about $78 million annually, the economic and health benefits resulting from pollution prevention could justify this investment (46). (See Box 5.3.)
In cities of the developing world, only a fraction of urban sewage is treated, even in cities in middle-income countries. Buenos Aires, Argentina, for instance, treats only 2 percent of its wastewater (47). The costs of collecting and treating urban sewage- -typically, about $1,500 per household for collection and primary treatment--are prohibitive for many developing countries. Costs are higher still to meet the additional treatment requirements of most developed countries (48).
Even in the United States, where major investments in sewers and treatment plants have already been made, the costs for completing and rehabilitating the existing infrastructure are calculated at $108 billion, and this does not reflect the full costs of removing nutrients from the effluent stream (49). In the United Kingdom, the cost of infrastructure needed to meet the new European water quality standards is estimated at $60 billion over the next decade, or about $1,000 per resident (50).
Lower-cost treatment options are clearly needed. These options should have some capability to remove nutrients as well as accomplish more traditional treatment goals. Alternatives range from modern marine outfalls that transport sewage into deep waters to the use of new low-maintenance equipment such as fine screens and special biological filters. New approaches to natural treatment systems such as sedimentation ponds and artificial wetlands with nutrient-scrubbing plants are promising for cities where sufficient land is still available (51) (52) (53) (54).
Another promising approach involves the reuse of municipal wastewater. Biosolids can be separated out, composted, and reused as fertilizer, for instance, while the treated effluent can be used to irrigate landscaping or crops or to feed aquaculture ponds. Effluent can also be used to recharge groundwater supplies, an approach that may be especially important in areas where saltwater intrusion into coastal aquifers has become a problem because of overdrafting of local groundwater supplies (55) (56) (57).
In Kochcice, Poland, a duckweed pond is being used to treat wastewater from 3,000 residents, at a cost far lower than that of a new wastewater treatment plant. The duckweed pond processes the wastewater, resulting in water quality at the outlet that is higher than Polish surface water standards require. Additionally, the biomass produced is harvested twice a year and used as feed for livestock (58). In Calcutta, India, 680,000 cubic meters of wastewater is discharged daily into 12,000 hectares of nearby wetlands. The wetlands are used for fish production, and the treated water is reused for irrigation. The E. coli count of the water entering the wetlands is about 10 million organisms per milliliter, whereas the treated effluent has an E. coli count of 10 to 100 per milliliter (59).
Innovative technologies alone will not suffice, however. Especially in the developing world, there is a critical need to develop the institutional capacity to plan, finance, and efficiently operate and maintain conventional wastewater treatment systems. For many cities, the volume of waste is too large, and the purification capability of wetlands too small, to rely solely on these methods of treatment. In addition, where wastewater also contains industrial wastes, new threats emerge from the bioaccumulation of heavy metals and other chemicals in fish and crops.
Cities are using a variety of regulatory and economic instruments to reduce industrial water pollution. Effluent charge systems, for example, impose fees on industrial facilities according to the quantity or quality of pollutants discharged. These systems are often more economical than regulatory mechanisms to induce firms to reduce pollution loads (60). The Netherlands has an effective water pollution charge system that provides a strong incentive for industries to reduce pollution. From 1969 to 1980, it is estimated that 50 to 70 percent of the pollution reduction in 14 industrial sectors was due to effluent charges (61).
Where possible, cities should encourage the separation of industrial wastewaters from domestic wastewater streams. Separate treatment of industrial wastes--or pretreatment before they are discharged to sewers--removes heavy metals and other toxics so that they do not contaminate domestic biosolids and wastewater that will be recycled. Separation and pretreatment also facilitate pollutant monitoring as well as the recycling of industrial wastewater, which reduces industrial water demand and the volume of wastewater discharged.
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