Proceed with Caution: California's Droughts and Desalination in Context

What is happening with desalination in California?

Desalination is the process of removing salt and other minerals from seawater, brackish water, wastewater, or contaminated groundwater to create pure water for drinking and other purposes. While desalination technologies vary, most modern plants use reverse osmosis, in which high volumes of saline water pass through membranes under high pressure to remove salts. The issue brief discusses seawater desalination that uses water from the ocean and brackish desalination that uses water that is more saline than freshwater, but less saline water than seawater. Brackish surface desalination plants use water from the tidal mixing zone of California's estuaries and bays and brackish groundwater desalination plants use water from underground aquifers.

Preferred Prioritization of California Water Resources

In California, brackish groundwater desalination plants significantly outnumber seawater desalination plants, both in number of facilities and in water produced. There are 23 brackish groundwater desalination plants in operation, with a combined annual capacity of 139,627 acre-feet per year. By comparison, there are 12 existing seawater desalination plants with a combined annual capacity of 62,840 acre-feet per year for all active facilities. One brackish surface water plant in the San Francisco Bay Area is under study for full-scale design, but there are currently no such plants in operation.

Recommendations

NRDC, California Coastkeeper Alliance, California Coast Protection Network, Orange County Coastkeeper, Heal the Bay, the Nature Conservancy, and Surfrider co-authored this paper as an overview of the science related to desalination and as a policy guidance tool. We demonstrate why conventional seawater and brackish surface water desalination should be reserved as the last option to address long-term droughts, while offering more affordable and sustainable alternatives.

  • Desalination should be considered as a last resort and only developed after all cost-effective water resources -- such as conservation, efficiency, stormwater capture, and recycling efforts -- have been implemented. These resources are less environmentally harmful, less expensive for the public, and typically require less energy than conventional desalination plants.
  • If these lower impact, less expensive options cannot meet local water demand, renewably powered groundwater desalination should be prioritized before considering more damaging conventional brackish surface water or seawater desalination facilities.
  • If conventional seawater or brackish surface water desalination facilities are pursued, they should be designed to minimize energy use, impacts on the electric grid, and indirect greenhouse gas emissions, and sited to mitigate adverse effects to sensitive marine and estuarine environments.