The Sacramento-San Joaquin Delta provides a third of Southern California's water supply to more than 25 million people, and it is in crisis. The largest estuary on the Pacific coast and the heart of California's water system, the delta has suffered a plummeting slide for almost a decade.

Litigation over delta ecosystem conditions led to federal court decisions to reduce water exports, and a serious, three-year drought made conditions for both the ecosystem and water supply even worse. The only way out of this downward spiral is to improve both the delta's environment and its water supply reliability.

I worked with other leaders in the California Legislature to craft a package of legislation that set a new course for California water policy, and especially for the delta. The 2009 Delta/Water Legislation addressed all of my "three C" priorities for water supply — conservation, capture and conveyance. We set high goals for urban water conservation — 20% by 2020 — and we set plans for developing the next generation of water capture and storage.

Finally, and perhaps most importantly, we set a path forward to address the most important water challenge facing California: conveying Sacramento Valley water across the delta through the State Water Project, for transfer to the San Joaquin Valley and Southern California via the Gov. Edmund G. Brown California Aqueduct.

The best prospect for the delta — and Southern California's water supply — is the Bay-Delta Conservation Plan (BDCP), now in development by the Brown administration. The BDCP is the critical link to our water future. It is the 21st century's "big idea" for the delta, and in scope and importance, BDCP rivals California's original 1960 decision to build the State Water Project.

BDCP will include both environmental and water infrastructure. The environmental infrastructure will include restored wetland and river habitat where salt and fresh water mix, creating a robust aquatic ecosystem. The water infrastructure will include a new way to separate the environment from water supply by building a conveyance structure from the Sacramento River to the water export facilities, either by a surface canal or an underground pipeline or tunnel.

California cannot afford to allow the BDCP to fail. The delta is too important to both our environment and our economy. Failing to make a decision on BDCP and allowing an earthquake to destroy delta levees — and the delta as we know it — will cost California far more.

Our economy will sputter to a stop, as both the Bay Area and Southern California wait for delta water supplies to be restored. BDCP is critical to California's water supply future. Every Californian needs to know its importance and support Gov. Jerry Brown's effort to complete the plan.

JOSE SOLORIO (D-Anaheim) is a California state assemblyman.