"Water, water everywhere; nor any drop to drink." Or so the conventional wisdom goes inregard to the vast water resource represented by the oceans of the world, as so eloquently statedin Samuel Taylor Coleridge's famous poem, The Rime of the Ancient Mariner. However,human ingenuity coupled with modern technology has begun to dispel this familiar aphorism, asseawater desalination has already become a well-established water treatment practice in someparts of the world. In some arid coastal regions where other water supplies are especially scarce,such as areas of the Middle East, the ocean has become a primary source of potable water. Still,despite technological advances and demonstrated effectiveness - high costs, concentrate disposalissues, and the availability of other raw water supplies have historically hindered seawaterdesalination from being implemented in the United States.The biggest impediment to seawater desalination in the U.S. has been the expense of treatment,whether in terms of capital costs such as equipment or the operational cost of the energyintensive processes. Even in the coastal areas of southern California, where the arid climate andhigh population density create seemingly ideal conditions for seawater desalination, thecontinued cost of pumping imported water over mountain passes via aqueduct networkshundreds of miles long has been considered more cost effective. And even if the cost ofseawater desalination were comparable to that of developing and treating other water sources, theenvironmental concerns associated with any potential concentrate disposal option have beenthought to be too significant and in any case non-permitable under any regulatory authority.However, while issues of cost and concentrate disposal remain primary concerns, the concept ofseawater desalination - particularly using reverse osmosis (RO) membranes - has gainedunusually rapid momentum in the normally conservative U.S. water treatment industry. In lessthan five years, the number of major water utilities either building, planning, or giving serious
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