With water in short supply in many California regions, local water agencies are looking to desalination to help stretch supplies. Improved technology to remove salt from brackish groundwater has made desalination an increasingly important tool for both augmenting supplies and improving water quality.
Thanks to funding made available by recent statewide bond measures, local agencies have secured financial assistance to move ahead with feasibility studies, pilot projects and other desalting activities. While some agencies have been desalting brackish water for decades, others are exploring it now as part of their integrated regional water management plans to help meet water resource management goals and objectives in their regions. Such plans may also include water recycling, increased water-use efficiency, groundwater storage and conjunctive use, and other local strategies.
CalDesal, a non-profit organization composed of water industry leaders, is working to promote brackish water desalination where feasible by advocating for funding and policies to expand use this important technology.
Brackish water refers to any water that is higher in salinity than fresh water but lower in salinity than seawater. It can be naturally occurring, such as in an estuary or from the intrusion of seawater into coastal groundwater basins, or from human activities, such as farming and other land uses.
In the desalination process, fresh water is produced by separating and removing salts and other impurities. Most desalination projects use one of two basic technologies. Reverse osmosis (RO) involves forcing brackish water through membranes or filters that screen out salt and other minerals. The second method is distillation, in which brackish water is heated to produce steam. The steam is then condensed, and the end product is water with a low concentration of salt and impurities.
Examples of brackish water desalination can be found in urban areas from the San Francisco Bay Area to San Diego. While most projects produce less than 5 million gallons per day (or 5,600 acre-feet per year), there are some larger-scale plants, with more expected in the coming years.
West Basin Municipal Water District, for example, operates the C. Marvin Brewer Desalter Treatment Facility to treat and purify brackish groundwater for potable use. Through a reverse osmosis treatment system, the Brewer Desalter produces 5 million gallons per day of high quality water to consumers.
Further inland, the Chino Basin Desalter Authority operates a desalination project that produces 14 million gallons a day of fresh water from brackish water pumped from wells throughout the Chino area. Brine left over from the process is transported by a regional brine line and subsequently discharged to the ocean.
In Northern California, the Alameda County Water District operates a series of wells that remove brackish water from groundwater. The district's Aquifer Reclamation Program was developed to stop the spread of saltwater already in the groundwater basin and to reclaim the aquifers of the basin for future potable use. Brackish water from some of the wells is treated at the Newark Desalination Facility rather than being allowed to flow back into San Francisco Bay. The soft water produced by the facility is blended with the harder water pumped from other parts of the groundwater basin to improve both the quality and reliability of the district's water supply.
Depending on the technology used, brackish water desalination can produce exceptionally high quality water by removing not only salts but also other contaminants such as nitrate. It can bring previously unusable water supplies online for beneficial uses and provide a "drought proof" source of water to help communities meet their water needs and reduce their reliance on imported water supplies.
Although the cost and energy requirements are coming down, brackish water desalination is still somewhat costly relative to other supply alternatives. There are also potential challenges associated with the disposal of brine produced in the desalination process.
In the Santa Ana River watershed, the Santa Ana River Watershed Authority has constructed a brine line to collect high salinity water throughout the upper watershed, convey it to advanced wastewater treatment facilities in Orange County and deliver the treated discharge to the ocean.
CalDesal believes brackish water desalination is one of many strategies that can play a role in boosting the state's water supply and overall reliability. Given the rising cost of building and operating surface water reservoirs and conveyance systems, and recent improvements in desalination technology, both ocean and brackish water desalination are likely to play a larger role in California's future.
CalDesal is a leader in advocating funding and policies that promote the use of desalination where feasible in California.