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Supplemental Water Purchases

San Luis Reservoir in California
San Luis Reservoir

Supplemental Water Purchases are delivered through State Water Project (SWP) facilities

Supplemental Water Purchases, Deliveries, and Storage

MWD relies heavily on Supplemental Water purchases from other agencies when local surface supplies are depleted or State Water Project (SWP) allocations are reduced.

For example, in 2018, MWD purchased 2,800 AF of supplemental water. This allows us to continue maximizing deliveries from San Luis Reservoir to Lake Cachuma, using pipeline capacity that would otherwise not be filled since State Water allocations are reduced.

Supplemental water purchases that remain stored in distant reservoirs year to year may be at risk of spill and / or  evaporation. In 2017, MWD initiated a regional groundwater banking program with Semitropic Water Storage District which allows us to store SWP deliveries and other supplemental water purchases without risk of spill or evaporation. This protects these purchases and improves water supply reliability. MWD currently has 900 AF stored in the Semitropic Groundwater Banking and Exchange program.  This water can be accessed in the future if / when needed.