Environmental Problems, Their Causes, and Sustainability 1

Desalination involves removing dissolved salts fromocean water or from brackish (slightly salty) water inaquifers or lakes. It is another way to increase suppliesof fresh water.One method for desalinating water is distillation—heating salt water until it evaporates, leaves behindsalts in solid form, and condenses as fresh water. Anothermethod is reverse osmosis—pumping salt water athigh pressure through a thin membrane with poresthat allow water molecules, but not most dissolvedsalts, to pass through. In effect, high pressure pushesfresh water out of salt water.There are about 13,500 desalination plants in 120countries, mostly the desert nations of the Middle East,North Africa, the Caribbean, and the Mediterranean.These plants meet less than 0.3% of the world’s waterneeds.Oil-rich and water-short Middle Eastern countriesproduce about 60% of the world’s desalinated water.Saudi Arabia is the largest producer and accounts formore than a third of the world’s output, followed bythe United States, which produces about a fifth of theworld’s desalinated water.Water-short Israel plans to get as much half of itswater from desalination by 2008. Some water-shortcoastal cities in the United States, such as Tampa,Florida, have built desalination plants to supplementwater supplies. In California, coastal cities such as LosAngeles, San Diego, and Monterey may build suchplants.There are two major problems with the widespreaduse of desalination. One is the high cost becauseit takes a lot of energy to desalinate water. Currently,desalinating water costs two to three times asmuch as the conventional purification of fresh water,although recent advances in reverse osmosis havebrought the energy costs down somewhat.The second problem is that desalination produceslarge quantities of briny wastewater that contains lotsof salt and other minerals. Dumping concentratedbrine into a nearby ocean increases the salinity of theocean water, which threatens food resources andaquatic life in the vicinity. Dumping it on land couldcontaminate groundwater and surface water.Bottom line: Currently, significant desalination ispractical only for water-short wealthy countries andcities that can afford its high cost.Scientists are working to develop new membranesfor reverse osmosis that can separate water from saltmore efficiently and under less pressure. If successful,this strategy could bring down the cost of desalination.Even so, it probably will not be cheap enough toirrigate conventional crops or meet much of theworld’s demand for fresh water unless scientists canfigure out how to use solar energy or other means todesalinate seawater cheaply and how to safely disposeof the salt left behind.Can Cloud Seeding and Towing Icebergsor Gigantic Water Bags Improve WaterSupplies? Solutions or Pipe Dreams?Seeding clouds with tiny particles of chemicals toincrease rainfall, or towing icebergs or huge bagsfilled with fresh water to dry coastal areas, probablywill not provide significant amounts of fresh waterin the future.For decades, 10 states, mostly in the water-short westernUnited States, and 24 other countries have experimentedwith seeding clouds with dry ice or tiny particlesof chemicals such as silver iodide. The hypothesisis that the particles become nuclei around which raindropsform and thus produce more rain or snow overdry regions and more snow over mountains.Bad news. First, cloud seeding does not work wellin very dry areas where rain is needed most, becausethere are few clouds to seed. Second, although someproponents in the multimillion-dollar cloud-seedingindustry say the technology works, a 2003 report bythe U.S. National Academy of Sciences says there is nocompelling scientific evidence that it does. Third, it introduceslarge amounts of the cloud-seeding chemicalsinto soil and water systems, possibly harming people,wildlife, and agricultural productivity.Fourth, seeding has led to legal disputes over theownership of cloud water. For example, during a 1977drought the attorney general of Idaho accused officialsin neighboring Washington state of “cloud rustling”and threatened to file suit in federal court.Some analysts have proposed towing huge icebergsfrom Antarctic or Arctic waters to arid coastal areassuch as Saudi Arabia and southern California andpumping fresh water from the melting bergs ashore.But nobody is sure how to do it, and even if they did itmight cost too much, especially for water-short developingcountries.In 2002, a company proposed collecting springrunoff water from several rivers in northern Californiaand piping it offshore to gigantic plastic (fiberpoly)bags as long as three football fields. Then tugboatswould carry the floating bags to southern Californiawhere the water would be piped to shore.The California Coastal Commission opposes thisscheme until the environmental impact can be assessed.The costs are unknown but would probably behigh enough that only wealthy areas could afford it.Stay tuned.15-7 REDUCING WATER WASTEWhat Are the Benefits of Reducing WaterWaste? A Win-Win SolutionWe waste about two-thirds of the water we usebut using water more efficiently could reducewastage to about 15%.322 CHAPTER 15 Water Resources