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.