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OD2S92 Needs and Problems Water Quality, Pollution Control, a nd Health Factors Status Throughout the Pacific Southwest, water quality varies greatly. The variation is due to municipal, industrial, and agricultural waste discharges; streamflow depletions by withdrawal for use; evaporation; and natural causes of pollutants. Federal, State, and local efforts are extensive in research, construction of waste water treatment plants, enforcement measures, basinwide pollution control planning, and other programs to reduce or eliminate water pollution. These activities have been greatly expanded in recent years, and their future expansion is expected. The quality of surface water deteriorates as it moves downstream and is used. In upstream reaches surface waters are generally of excellent quality. Downstream reaches of major streams, terminal lakes, bays, and coastal waters are subject to water quality degradation primarily by municipal, industrial, and agricultural uses and by natural causes. High sediment and turbidity loadings, spills of oil and hazardous materials, waste materials from vessels, and pesticide residues also contribute to the Pacific Southwest's surface water quality problems. Groundwater quality is highly variable, and in some locations is inadequate for many uses. Additional municipal and industrial waste treatment plants - and improvements of many of the existing plants - are required to insure conformance with water quality standards, and to accommodate the increasing popuiation and the expanding economic activity. Water quality control practices are directed toward: (1) treatment of point source wastes prior to discharge to adjacent bodies of water; (2) transfer of treated wastes to water bodies of greater assimilative capacity; (3) reclamation and direct reuse principally for recreation; and (4) evaporation and percolation into the ground. Salinity improvement measures are very rare. The inadequate treatment of municipal waste discharges, and the lack of collection and treatment facilities in some rural and recreational areas cause public health problems periodically. In some locations encephalitis has occasionally been a significant problem. It is checked by extensive mosquito control programs in the heavily irrigated areas. The need for water of suitable quality is common to almost every facet of today's civilization. Yet almost every use made of water tends to alter its quality in one way or another. In this report, predicting future water quality in specific locations is, in some cases, the result of refmed and elaborate studies. But in most instances, predictions are based on general relationships and judgment. Future water quality problems usually can be expected to be similar to existing problems. For example, the expected population increase from 21.5 million persons in 1965 to 65.8 million in 2020, along with attendant industrial activity, can be expected to produce a proportionately larger volume of waste material. The great bulk of this population will be located in the middle and southern coastal zone of CalifornIa, roughly from San Francisco to San Diego, including some inland population centers. Water quality in coastal waters, bays, and especiaily estuaries is uniquely subject to the activities of man because the major concentrations of population and economic activity occur adjacent to these waters or immediately upstream. Increasing concern has been expressed over the effects of municipal and industrial waste discharges upon several receiving waters, including San Francisco Bay and Los Angeles Harbor. Restoration of water quality in San Diego Bay has demonstrated the beneficial effects of eliminating or greatly reducing major waste discharges into semiconfined waters. Other water quality problems are caused by the intensive use of confined waters by commercial, military, and pleasure craft, resulting in floating petroleum products, trash, garbage, and untreated human wastes. Also, in some confined waters concentrations of pesticides and heavy metals are excessive. The increaseSln thermal-electric power production projected for the future will require an enormous quantity of waste heat to be dissipated, mostly in the coastal waters. The capacity of the Pacific Southwest's waters to assimilate the waste heat has required changes in present methods of heat disposal with all inland plants projected to utilize cooling towers or ponds. Water resource development has a profound two-way effect upon estuaries: (1) the reduction of 67