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-10- I I I . I I I , I I I I I I I I I I l Water Availabilitv for HuniciDal and Industrial Uses During the primary data collection effort performed to support development of water demand projections, information was obtained to allow quantifica- tion each water provider's available water supplies. Based on the infor- mation obtained, water supplies were quantified for each water provider in terms of average and safe annual yields. A thorough review and modification process was again followed to ensure that each water providing entity was in agreement with, or at least understood the basis for, the quantification of water supply yields. Each entity was encouraged to review estimated average and safe annual yields, and modifications were made on the basis of discussions with individual water providers. Criteria for Average and Safe Yields For the purposes of this study, the average annual yield of a particular entity's water supply was defined as the total supply, as of 1988 in most cases, that would be available to that entity during a year of average hydrologic conditions, as defined by that entity. Safe annual yield for a particular entity equaled the minimum total supply that would be available in a single year during a specified drought, as defined by that entity. A single specified criterion for safe annual yield was not uniformly used by water providers throughout the study area. However, the most consistent approach was to define safe yield in terms of the minimum annual yield during the 1950s drought. This definition was loosely applied to the total safe yields determined during this study. For each entity not having a specified criteria for safe yield, the lowest total supply, again as of 1988 in most cases, that would have been available in a single dry year during the 1950s drought (1954) or the 1970s drought (1977) was taken as the safe annual yield.