Man's control of water quality.

Man has certain needs for water: physiological, domestic, agricultural and industrial. These needs are not the same in quantity or quality, in location or in time, yet they must all be met to allow for mankind's full development. Man's use of water degrades its quality: by gross pollution, by residual materials which change the ecology of the water environment, and by persistent microchemical pollutants which may pose both long and short-term health hazards. Man can control water quality; but first he must measure it. The criteria of acceptable quality, particularly for the protection of public health, are continually being refined; already certain contaminants are considered a hazard at the femtogram per litre level, i.e. a million-millionth of thefamiliar p.p.m. Even when he can measure such quantities, man must protect or treat the water to maintain the required quality standards. The future will require refined micro-level measurement, toxicity and carcinogenic screening methods, and further consideration of water-distributed prophylaxis. Serious consideration must be given to new concepts in water management: multiple re-use, parallel supply systems and integrated treatment processes. MAN'S NEEDS FOR WATER Water is essential to life. Water is essential to living. Water is essential to civilization. Man's needs for water are physiological, domestic, agricultural and industrial. Fortunately these needs are not identical with regard to water quantity or quality, and they are not identical in location nor in time. These needs must be balanced so that water may be apportioned to allow for mankind's full development.