Inland waters occur in strictly limited volume (about 0.01% of global flow in rivers and their associated lakes and swamps), they undergo both seasonal and yearly fluctuations, and they are subject to man-made changes in their physical and biological qualities. Inland water bodies also suffer over-enrichment (eutrophication) and pollution caused by discharges from industries, drainage from agricultural and domestic chemicals and wastes, and acidification from acid rain.
Adverse impacts on freshwater systems are of critical concern given both the scarcity of and increased demand for water. The flow of many river systems has been regulated by storage dams, or by structures associated with the inter-basin transfer of water. Salinisation, eutrophication, and pollution by heavy metals, mine dump effluents, pesticides, insecticides and herbicides have considerably reduced both surface- and ground-water quality. Catchment changes through afforestation, alien plant invasion, irrigation and over-abstraction, and human settlement have reduced natural run-off and groundwater levels substantially.
During the 1970s there was a world-wide increase in the absolute numbers of people without access to safe water or sanitary facilities. Increased eutrophication and pollution of inland water bodies have been only partially offset by the biological revival of some rivers and lakes through various remedial and control measures. The continuing growth of the world population and acceleration in water use had by 1970 already begun to strain the water resources of some areas, and the problems were aggravated by pollution and the continued prevalence of water-borne disease. Withdrawals of water for use in agriculture, industry and in the home continued to increase during the decade, although in many developed countries more slowly than in the preceding decade. Statistics remained uneven, but domestic water supplies barely kept pace with population growth in many developing regions, and waste water disposal services fell behind in many areas. Ground-water quality also deteriorated in many areas, and statistics for this section of the freshwater resource remained inadequate.
Whereas in developing countries the proportion of the urban population with access to safe water supply rose from 67% in 1970 to 77% in 1975 and then declined slightly to 75% in 1980, although the proportion of rural people served by safe water supply increased from 14% in 1970 it had still reached only 29% in 1980. The waste water treatment situation was even less heartening. While a high proportion of the developed urban populations had adequate services, the proportion of developing country urban population served by sewers and other sanitary facilities declined during the decade, from 71% to 53%. In rural areas the numbers served were 11% in 1970 and little better (13%) in 1980.
The total water use in 1980 was in the order of 2,600 to 3,000 km3/year; this is projected to have reached 3,750 km3 in 1985 - about 8 to 10% of the average run-off in all continental river basins. The three major uses of water are: irrigation (73%), industry (21%) and domestic and recreational uses (6%). The 1970s saw further extension of irrigation (and improved drainage) to newly reclaimed lands, especially in arid regions. Industrial uses increased during the decade, but savings were also made through increased efficiency. In Japan, for example, total industrial withdrawals increased from about 50 million cubic metres in 1974, but by the mid-1970s two-thirds of this was recycled water compared with one-third in 1965. Total water demand for the year 2000 is predicted to be between two and four times that for 1970.