Conjunctive use is the coordinated management of surface water and groundwater supplies to maximize the yield of the overall water resource. An active form of conjunctive use utilizes artificial recharge, where surface water is intentionally percolated or injected into aquifers for later use. A passive method is to simply rely on surface water in wet years and use groundwater in dry years. More than 65 water agencies in the state operate groundwater recharge programs. The success of many of these programs, however, depends on purchasing available surface water from other users.

Conjunctive use is becoming a key part of the state’s overall water management strategy in terms of coping with a growing population.

Conjunctive use is becoming a key part of the state’s overall water management strategy in terms of coping with a growing population. In southern California basins, about 21.5 million acre-feet of additional conjunctive use potential is available, according to the Association of Ground Water Agencies. The amount represents enough water to fill Diamond Valley Lake, the region’s largest reservoir, 26 times over.