Thus, desalination has received increasing attention in drought years when water supplies become greatly threatened or diminished. In above-average water years, permit requests for desalination facilities are infrequent. The current drought-response approach to desalination forces government agencies to conduct expedited review of these facilities during scarce water periods. Currently, neither the State nor most local governments have long-term planning mechanisms regarding use and potential environmental impacts of desalination plants for potable water production. 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. 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. However, certain characteristics about desalination make it an extremely costly technology. Capital investment and operations are expensive for all desalting options because pipes and equipment require corrosion-resistant materials, while special pretreatment filters and cleaning membranes require frequent backwashing to remove the rapid accumulation of solids.