淡水稀缺已经成为全世界超过10亿人的主要问题，主要是在干旱的发展中国家。世界卫生组织预测，到本世纪中叶，我们有40亿人 – 占世界目前人口的近三分之二 – 将面临严重的淡水短缺。根据非营利性食品和水资源观察，淡化海水是最昂贵的淡水形式，考虑到收集，蒸馏和分配淡水的基础设施成本。该小组报告说，在美国，淡化水的成本至少是其他淡水来源的五倍。类似的高成本也是贫穷国家海水淡化工作的一大障碍，因为有限的资金已经过于紧张。预计到2050年，人口数量将增加50％，资源管理者越来越多地寻求替代方案来遏制世界日益增长的口渴。海水淡化 – 一种将高压海水推入微型膜过滤器并蒸馏到饮用水中的过程 – 被一些人认为是最有希望解决问题的方法之一。但批评人士指出，没有经济和环境成本，它就没有了。在环境方面，广泛的海水淡化可能会对海洋生物多样性造成严重影响。 “海水中充满了生物，其中大部分都是在海水淡化过程中丢失的，”世界上最重要的海洋生物学家之一西尔维亚·厄尔（Sylvia Earle）说道。 “大多数都是微生物，但海水淡化厂的进水管也占据了海洋中生命横断面的幼虫，以及一些相当大的生物……这是开展业务的隐性成本的一部分，”她说。厄尔还指出，海水淡化留下的非常咸的残留物必须妥善处理，而不是仅仅倾倒回海中。食品和水观察同意，警告说已经受到城市和农业径流影响的沿海地区不能承受大量浓缩盐水污泥。食品和水观察主张改善淡水管理实践。 “海水淡化隐藏了日益增长的供水问题，而不是专注于水资源管理和降低用水量，”该组织报告援引最近的一项研究，该研究发现加州可以通过实施具有成本效益的城市用水满足未来30年的用水需求保护。海水淡化是“一种昂贵的，投机性供应选择，将从更实际的解决方案中消耗资源，”该集团说。当然，最近加利福尼亚州的干旱让每个人都回到了他们的绘图板，海水淡化的吸引力已经恢复。 2015年12月，在圣地亚哥北部卡尔斯巴德开设了一家为110,000名客户提供水的工厂，报告费用为10亿美元。海水淡化的做法在世界范围内变得越来越普遍。自然资源保护委员会的Ted Levin表示，已有120多个海水淡化厂在120个国家供应淡水，其中大部分位于中东和加勒比地区。分析师预计，未来几十年全球淡化水市场将大幅增长。环保倡导者可能只需要尽可能地推动“绿化”这种做法，而不是完全消除它。
Freshwater scarcity is already posing major problems for more than a billion people around the world, mostly in arid developing countries. The World Health Organization predicts that by mid-century, four billion of us — nearly two-thirds of the world’s present population — will face severe fresh water shortages. According to the non-profit Food & Water Watch, desalinated ocean water is the most expensive form of fresh water out there, given the infrastructure costs of collecting, distilling and distributing it. The group reports that, in the U.S., desalinated water costs at least five times as much to harvest as other sources of fresh water. Similar high costs are a big hurdle to desalination efforts in poor countries as well, where limited funds are already stretched too thin. With human population expected to balloon another 50 percent by 2050, resource managers are increasingly looking to alternative scenarios for quenching the world’s growing thirst. Desalination — a process whereby highly pressurized ocean water is pushed through tiny membrane filters and distilled into drinking water — is being held forth by some as one of the most promising solutions to the problem. But critics point out it doesn’t come without its economic and environmental costs. On the environmental front, widespread desalination could take a heavy toll on ocean biodiversity. “Ocean water is filled with living creatures, and most of them are lost in the process of desalination,” says Sylvia Earle, one of the world’s foremost marine biologists and a National Geographic Explorer-in-Residence. “Most are microbial, but intake pipes to desalination plants also take up the larvae of a cross-section of life in the sea, as well as some fairly large organisms…part of the hidden cost of doing business,” she says. Earle also points out that the very salty residue left over from desalination must be disposed of properly, not just dumped back into the sea. Food & Water Watch concurs, warning that coastal areas already battered by urban and agricultural run-off can ill afford to absorb tons of concentrated saltwater sludge. Food & Water Watch advocates instead for better freshwater management practices. “Ocean desalination hides the growing water supply problem instead of focusing on water management and lowering water usage,” the group reports, citing a recent study which found that California can meet its water needs for the next 30 years by implementing cost-effective urban water conservation. Desalination is “an expensive, speculative supply option that will drain resources away from more practical solutions,” the group says. Of course, the recent California drought sent everyone back to their drawing boards, and the appeal of desalination has revived. A plant providing water for 110,000 customers opened in December 2015 in Carlsbad, north of San Diego, at a reported cost of $1 billion. The practice of desalinating salt water is becoming more common worldwide. Ted Levin of the Natural Resources Defense Council says that more than 12,000 desalination plants already supply fresh water in 120 nations, mostly in the Middle East and the Caribbean. And analysts expect the worldwide market for desalinated water to grow significantly over the coming decades. Environmental advocates may just have to settle for pushing to “green” the practice as much as possible in lieu of eliminating it altogether.