Desalination is often misunderstood to mean only the removal of sodium chloride (salt) from brackish or salt water, yet with today's technology desalination can virtually remove any mineral and most biological or organic chemical compounds. More appropriate terms for desalination might be "de-mineralization" or "purification" of water. Discharges to ocean and coastal waters from desalination plants is a concern for ocean resource management.
Desalination facilities use two basic technologies to extract potable water from seawater. Reverse osmosis works by forcing seawater through a semipermeable membrane, which restricts salt and other minerals, but allows water molecules to pass through. The second method is distillation where seawater is heated to produce steam, which is then condensed to produce water with a low salt concentration and few of the other impurities contained in the original water. Depending on the technology used, the final water product is generally high quality, ranging from 1 to 500 parts per million total dissolved solids (the recommended California drinking standard for total dissolved solids is 500 milligrams per litre maximum, which is equivalent to 500 parts per million).
Desalination plants located in the coastal zone fall under the jurisdiction of the California Coastal Act, administered by the California Coastal Commission. If a facility were to be proposed in the San Francisco Bay Area, it would fall within the jurisdiction of the San Francisco Bay Conservation and Development Commission. Discharge of liquid brine waste from desalination operations is regulated under the 1987 amendments to the Clean Water Act through the National Pollutant Discharge Elimination System (NPDES) administrated by the State's nine Regional Water Quality Control Boards (RWQCBs). In addition, the RWQCBs issue Waste Discharge Requirements through Porter-Cologne Water Quality Control Act authority. Other State agencies having some role over the planning, environmental review, or operation of desalination plants include air quality management districts; the California Energy Resources, Conservation and Development Commission; and the California Departments of Fish and Game, Water Resources, and Health Services.
This file last modified on: Tuesday, January 24, 2006.