This report presents a summary view of the water-supply situation in the nine counties that comprise the San Francisco Bay region, California, and thereby provides water data, based on 1970 conditions, that are needed for regional planning. For the purpose of this study the nine-county region has been divided into 15 subregions on the basis of hydrologic and economic considerations. Firm water supply is tabulated for each subregion by source--ground water, surface water, and imported water. Water demand in 1970 is tabulated for each subregion by type of use or demand--public supply, rural self-supply, irrigation, self-supplied industrial water and thermoelectric power generation.

The San Francisco Bay region is dependent to a large degree on imported water. Under 1970 conditions of development, the firm water supply is 2.2 million acre-feet per year; of that quantity, almost 1 million acre-feet per year is imported water. The water demand in 1970 was 1.9 million acre-feet, about half of which was consumed. Under 1970 conditions of water development and use, a series of dry years would probably necessitate some curtailment of irrigation activities in four of the subregions, where the bulk of the demands i for irrigation water. Under those same conditions there is generally ample water for municipal and industrial use throughout the region, except in eastern Marin County where the firm municipal supple does not exceed the 1970 demand for municipal and industrial water.

Although the firm water supply of the San Francisco Bay region, including imported water, is generally adequate to meet present needs, supplemental supply will be required to meet increased demand in the future. The expansion of existing surface-water facilities and the construction of new surface-water projects, now considered feasible, could provide a combined firm supplemental yield of slightly more than 1 million acre-feet per year, almost three-fourths of which would be available for import by those subregions that might experience a water deficient in the future. However, any supplemental water that might be developed by such alternative methods as desalination of brackish or salt water, weather modification, and various conservation measure, will correspondingly reduce requirement for supplemental water from the more conventional sources.

The aspect of water quality is not discussed in this paper. Because of the present availability of imported water of good or acceptable quality, water quality, as it affects the supply, is not a serious problem at this time, except perhaps in local areas adjacent to San Francisco Bay and in the Sacramento-San Joaquin Delta. In those areas ground water has been degraded by salinity intrusion. Although the prediction of future trends in population, land use, and water demand is beyond the scope of this report, there is not doubt that vigilance and careful planning will be required to prevent serious future deterioration of the quality of the water supply.