Key Issues in Seawater Desalination in California: Marine Impacts

Desalination, like other major industrial processes, has environmental impacts that must be understood and mitigated. A new report from the Pacific Institute examines effects on the marine environment associated with the construction and long-term operation of seawater desalination plants, including withdrawing water from the ocean and discharging the highly concentrated brine.

“If and when we build plants in California, we must ensure that the plants are built to the highest standards given what we know now,” said Cooley. “Additionally, monitoring of existing and proposed desalination plants is crucial to improving our understanding of the sensitivity of the marine environment and helping promote more effective operation and design to minimize ecological and biological impacts in the future.”

Modern reverse-osmosis desalination plants, such as those planned or proposed on the California coast, take in large volumes of seawater – generally two gallons are withdrawn for every gallon of freshwater produced – and pass it through fine-pored membranes to separate freshwater from salt. The highly concentrated brine is then typically disposed of back into the ocean.

With the majority of desalination plants extracting water directly through open water intakes in the ocean, there is a direct impact on marine life. Fish and other marine organisms are killed on the intake screens (impingement); organisms small enough to pass through, such as plankton, fish eggs, and larvae, are killed during processing of the salt water (entrainment). The impacts on the marine environment, even for a single desalination plant, may be subject to daily, seasonal, annual, and even decadal variation, and are likely to be species- and site-specific.