Water scarcity can be addressed, in part, through conservation and recycling as well as through better use of conventional resources. Modern seawater desalination technology is a sustainable new source of fresh water, however, that should be a component of any program designed to address long-term water supply needs.

2 SEAWATER REVERSE OSMOSIS
Reverse osmosis is a water desalination process that produces drinking water by forcing seawater against a semi-permeable membrane, producing pure water on one side and concentrated brine on the other. Reverse osmosis is widely used around the world; indeed, reverse osmosis processes accounted for 59% of contracted desalination capacity as of September 2008, having grown at a rate of 17% per year since 1990.

Reverse osmosis processes, however, can be energy-intensive because of the high pressures that must be attained for it to work effectively. In seawater reverse osmosis (SWRO) systems, an operating pressure of 870 to 1015 psi is required. Even at these pressures a maximum of approximately 50% of the available pure water can be extracted before the osmotic pressure becomes so high that additional extraction is not economically viable. The rejected concentrate leaves the process at nearly the membrane-feed pressure. The combination of the high required membrane-feed pressure and the high-volume reject stream has historically limited the deployment of large-scale SWRO to regions where power is inexpensive and abundant.