Fresh water

Abundance or scarcity of water can mean prosperity or poverty, life or death. It can even be a cause of war. Most countries have deeply worrisome problems concerning the quantity and quality of their fresh water resources, and many countries are suffering from the effects of pollution of their coastal waters. Constraints on the supply of fresh water are increasing, aggravated by droughts, depletion of aquifers, and deforestation, while demand for water is rising rapidly for irrigation, energy generation, industrial production, and urban consumption.

The availability of fresh-water resources per capita varies widely. Many areas of the world are semi- arid, suffering a devastatingly high rainfall variability and recurrent droughts as well. The largest such area, with a rainfall variability of over 40 per cent, consists of North and sub- Saharan Africa, the Arabian peninsula, the southern part of the Islamic Republic of Iran, Pakistan and western India. In the Sahel rainfall is not only unreliable, but is less now than 50 or even 30 years ago. Water supply per capita in Asia is less than half the global average, and the continent's run-off is the least stable of all the major land masses. In Africa two- thirds of the countries have at least one- third less run-off than the global average. But the main problem is under- development of water resources relative to needs and potential, and the uneven distribution of water resources.

In spite of the large increases foreseen in water withdrawals for irrigation, industrial, and domestic uses, total use worldwide in the first half of the 21st century is likely to be less than half the stable renewable supply at the global level. In North Africa and the Middle East, however, meeting the expected demands by the year 2010 could require virtually all of their usable fresh-water supplies. Even under existing patterns of water use, the amount of water needed in Western Asia has doubled in the last 20 years. In several countries, including Bahrain, Democratic Yemen, Kuwait, and the Syrian, Arab Republic, total demand for water already equals or exceeds the available supply, or is expected to do so by the year 2010. Use in southern and eastern Europe as well as central and southern Asia also could closely approach the limits of available supplies that can be safely tapped.

At least 19 developing countries in 1975 had total natural water supplies of less than 500 cubic metres per person per year. This translates into some 200 cubic metres or less of actual availability, taking into account losses incurred in the process of tapping and harnessing the natural supplies for particular uses. Ten more countries could be in a similar situation by the year 2000, and another eight by the year 2025. Still others would have less than 1,000 cubic metres per person available per year and could thus be regarded as approaching a situation of severe scarcity.

From 15 to 25 North African and sub-Saharan African countries may face serious problems with water shortages by the year 2025. Most of these countries have agricultural sectors that need higher than average inputs of water and fertilizer for food self-sufficiency. Food self- sufficiency will be an elusive goal as household and industrial demands for water will compete strongly with the agricultural sector for the limited quantities of water available. Turning to water quality, contamination of water supplies is posing health risks and is drastically increasing the costs of water treatment facilities. Polluted inland water bodies and seas are reducing the productivity of fisheries and increasing the health risks of eating fish caught in those waters. Polluted irrigation water poses health risks, undermines long-term crop productivity, and degrades the recreational use and aesthetic aspects of surface water. Surface and underground water sources in many areas are contaminated by fertilizers, herbicides and pesticides used in agriculture,  and by industrial and residential waste,  seepage from waste storage and disposal sites, and acid rain. Toxic chemicals have killed large amounts of aquatic biota and rendered many water sources useless for drinking and even for irrigation.

In the industrial world, where new waste-water treatment facilities have been built in recent years at considerable cost, river water quality has improved in some cases. However, long stretches of numerous rivers still remain heavily polluted. The run-off of pesticides, herbicides, and fertilizers from agricultural lands has become a major problem in such sources of community water supply as artificial lakes and reservoirs, especially in several countries in Latin America.

Most urban centres in the developing countries lack adequate facilities for the collection and disposal of domestic and industrial wastes. This results in urban run-off highly polluted with pathogens and organic materials that may have a serious impact on the quality of nearby surface waters and shallow ground waters. In many cities, open sewers and surface run-off after rain create "rivers of sewage" that contaminate local water supplies.

One of the most acute problems is the increasing flow of nitrates into drinking waters, leading to possibly serious threats to human health. This problem is already widespread in areas of intensive agriculture in Europe and is appearing in the USA and the USSR. The increasing use of fertilizers in the developing countries implies that similar problems can be expected there also. Nitrogen and phosphorus, the two most important causes of excessive plant growth in surface water supplies, are well above natural levels in the water measured by the Global Environmental Monitoring System (GEMS). This project consists of 344 monitoring stations in 59 countries. Many rivers outside Europe contain 2.5 times as much nitrates as the natural average for unpolluted rivers, and levels in European rivers are 45 times higher than natural background levels. Relatively high levels of organochlo-rine pesticides and the polychlorinated biphenyls (PCBs) were reported by stations in China, Japan, and the United Kingdom. Very high levels were found in Colombia, Indonesia, Malaysia, and the United Republic of Tanzania. OECD time-series data show that biological oxygen demand (the amount of oxygen needed to decompose sewage and other organic wastes) declined in some rivers and increased in others. Nitrates increased in most major rivers and lakes from 1975 to 1985, but phosphate concentrations either remained stable or declined slightly. In most OECD rivers there was a marked drop in concentrations of lead, cadmium, chromium, and copper.

Concern about the protection and rational management of coastal water and marine resources has increased in many countries in the past few years. Shorelands, small islands, coral reefs, estuaries, seagrass beds, and open coastal water foster great varieties of fish and other marine organisms. They also have scientific and educational value and attract tourism. Outbreaks of algal blooms in coastal waters, as well as problems of sewage disposal, have focused the attention of governments on the need for marine environment protection. The incineration of chemical wastes at sea has also triggered considerable concern. In 1987, eight North Sea countries agreed to reduce waste incineration at sea by at least 65 per cent by the end of 1990 and to phase it out altogether by 1994. This target has not been achieved.

In order to ensure that the finite amount of fresh water in the hydrological cycle is adequate to meet the growing demand, new ways must be found to conserve water and to implement existing methods more extensively. New water supplies must also be developed, taking into account likely adverse effects on the environment. Reuse of waste water has been advocated mainly for non- potable purposes, such as agricultural irrigation, cooling, and industrial in- plant recycling. A large proportion of the water used for industrial purposes can be recycled several times, and the efficiency of water use can be increased further by using integrated water recycling systems. Given the typically low price of industrial water supplies relative to prices of other inputs, incentives for using water more efficiently must come from strict water allocations and stringent pollution control requirements, as well as from more rational pricing policies.

The scope for waste water reuse is relatively small so far in developing countries, as many of them do not have sewerage systems that collect it. But there is wide scope for their new industries to have built-in water recycling systems. Developing countries are probably better placed to take advantage of new recycling technologies than the older industrial countries, because building water efficiency and pollution control into new plants is generally much cheaper than retro-fitting old ones. Some of the technologies available are capable of reducing water use and waste water flows by up to 90 per cent. Technology transfer could help to alleviate water supply and pollution problems in the emerging industrial countries.

Raising the efficiency of irrigation is even more important. Irrigation accounts for the bulk of most countries' water use and is generally rather inefficient. Improvements in technical infrastructure and adoption of more efficient management methods, such as lining irrigation canals, can greatly reduce seepage losses. Even more effective would be to educate farmers on optimal use of water, such as avoiding using more water than necessary through assessment of water needs for different crops at various places and times. Co- ordination of the use and management of groundwater and surface water can significantly increase the total efficiency of irrigation. Other options are the use of brackish water and treated waste water for irrigation of salt-tolerant crops and for certain industrial uses.

Although municipal use of water is much less than irrigation and industrial use, the costs of supplying safe drinking water as well as collecting and treating household waste water are large. This is especially so in comparison with per capita incomes in the low- income countries. Conserving water and increasing the efficiency of household and municipal water use would reduce the need for new plants, water mains, and sewer pipes. It would also cut energy and other costs for providing and disposing of municipal water supplies. Efficiency can be increased by reducing losses in the distribution system and using less wasteful designs for new, improved household fixtures and appliances. Domestic waste water could be collected, treated, and used for agricultural purposes.

A region's fresh water also can be conserved by cutting loss through evaporation—by using underground or covered storage instead of storage in open surface reservoirs. The costs, while high, often seem reasonable compared to alternative schemes.

Several technically feasible and economically viable new options are available for increasing fresh water supplies. Of the non- conventional ways, such as seeding clouds to induce precipitation, towing icebergs,  desalting sea and brackish water,  and transporting water by tankers, the latter two appear to hold the greatest near- term potential. But the available desalination technologies (distillation, electrodialysis, and reverse osmosis) are highly energy-intensive and far too expensive, except for countries having non-marketable supplies of natural gas or for islands that depend on tourism for a large share of their income.

The seas

Almost all important stocks of bottom-dwelling fish species are either fully exploited or over- fished; most stocks of the valuable crustacean species, especially shrimp, are also heavily exploited and have generally reached a stage of economic over-fishing, although there is significant potential for aquaculture. There are better prospects for increasing the harvest of small surface-dwelling species; however, the stocks of such species, some used primarily for conversion into fish meal and oil, are subject to considerable long-term fluctuation in abundance. Sustained growth in demand, given these supply constraints, will lead to a continued rise in the real prices of preferred species.

The growing demands on the fisheries sector, particularly for human consumption, could be satisfied by several changes in commercial fishing practices that could significantly increase the supply of fish. These include saving the discards from trawling operations for preferred species, reduction of post-harvest losses through better landing, storage, and marketing facilities, and the wider use of small surface-dwelling species for human food products. Major gains also may be obtained from the culture of additional species through extensive aquaculture systems and fishery enhancement in reservoirs, lakes, and even in the open seas.

Extension of national jurisdiction over fisheries, whilst a precondition for rational management, does not of itself ensure the most efficient conservation and use of fish stocks. It must be reinforced with the legal and operational institutions necessary to design and implement conservation and management schemes. Greater support for fish farming and other types of aquaculture— for example, the award of fishing rights to specific communities—could make a significant nutritional and social impact in rural areas of low- income countries. Such rights often reflect traditional customs that have demonstrated the value of allocating exclusive fishing rights in defined areas to specific groups of fishermen, with the attendant incentive of maintaining sustained production through self-regulation and control.