There’s a problem with a network of levees at the center of California’s plumbing; a freshwater confluence called the Sacramento-San Joaquin River Delta. Most of the state’s water is drawn from the delta, which is protected by poorly constructed levees from another era. If enough were to breach, say from an earthquake or severe storm, sea water from San Francisco Bay could rush in, tainting the water supply for two-thirds of California. If the levees were to crumble, 25 million people would be left, maybe not high, but definitely dry.

The bulk of California’s water flows into the Sacramento and San Joaquin rivers. The two rivers meet east of San Francisco Bay in a tidal marsh with over seventy inhabited islands. Groundwater pumping is a contributing factor to the sinking of most of these islands below sea level. Delta islands are like bowls surrounded by levees, according to Dave Mraz, Chief Levee Engineer for the State Department of Water Resources, and if these levees go, the bowls will fill with water. More than 160 levees have breached in the Delta since 1900 and many of these breached islands now remain as levee-top lagoons instead. People not only live on many of these islands but their levees also protect California’s water supply.

California has two pumping stations at the southwest end of the delta, approximately fifty miles east of San Francisco that delivers water from Northern California to Southern California along a 444 mile aqueduct. By using these pumps, the Delta is able to serve California’s agricultural industry and municipal water to numerous cities. The water first has to pass between many miles of levees before making it to the pumps, and if a levee is breached, the water rushes in. If you have enough levee failures at once, too much salty ocean water rushes in and the pumps shut down.

El Nino storms aside, what about a big earthquake? The levees, it turns out, are extremely vulnerable, having been constructed over the past 150 years or so by Delta settlers from sand, silt, peat and rocks. Farmers have continued piling the levees higher in a similar process, without reinforced slopes and concrete foundations, causing U.C. Berkeley Professor of Civil Engineering, Robert Bea to refer to the infrastructure protecting two-thirds of the state’s water as “antiquated piles of dirt.” A large enough El Nino inspired storm could take out numerous levees, but a strong earthquake could be catastrophic. According to reports, solving the water supply issue would take $25 billion and ten years - while still failing to address non-water infrastructure issues along the levees, agriculture and the people in those areas. For now, the solution is “patch and pray” as Professor Bea puts it.