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82 Part i california Water <br />capacity is already abundant, but aquifers recharge and empty far more slowly <br />than surface reservoirs, making them more suitable for long-term or dry-year <br />storage. Withdrawal from aquifers typically requires pumping. In California, <br />much recharge is a by-product of crop irrigation, although natural streams <br />and precipitation also contribute. Increasingly, artificial recharge programs are <br />employed. These programs spread surface water over dedicated recharge fields <br />or inject it into wells. Conjunctive use programs, which manage surface water <br />and aquifers jointly, make it possible to expand the system’s overall capacity, by <br />storing more water in aquifers during wet years for use in dry years. Although <br />such programs are expanding, the ability to fully exploit the system’s potential <br />is limited by the lack of comprehensive aquifer management in many regions, <br />cumbersome institutional rules regarding surface reservoir operations, and <br />limited synthesis of technical information regarding the capacity and condition <br />of groundwater basins (Chapter 6). <br />As an illustration of this last point, DWR’s occasional bulletin on the <br />state’s groundwater basins, Bulletin 118, has been issued only twice since 1980. <br />These reports include little analysis or strategic overview of the condition of <br />California’s aquifers, how they are employed, or how their management could <br />improve. For instance, although DWR gathers data on over 400 aquifers in the <br />state, these data are not maintained in a way that allows statewide or regional <br />assessments of aquifer conditions, such as overdraft or contamination. <br />Water Quality Concerns <br />It is not enough to have “enough” water. Water must also be of adequate quality <br />for each use, either in its natural state or with affordable treatment. <br />Different qualities for different purposes <br />Different uses often require different types of water quality. Urban water users <br />require the highest water purity, and costs of treatment increase when the <br />quality of water sources is lower. Drinking water quality standards are being <br />tightened and treatment facilities upgraded as additional contaminants are <br />identified and studied (Calder and Schmitt 2010). This trend is likely to continue <br />and perhaps accelerate, as understanding of public health and water chemistry <br />improves (Chapter 3). <br />Agricultural water users face significant, but less constraining, water quality <br />concerns, mostly involving excesses of salinity and minerals such as boron that <br />reduce crop productivity and limit crop choices.