我的一个朋友住在印度最富裕的城市之一新德里一个中产阶级社区。尽管该地区每年有相当多的降雨，但他早上醒来时却听到扩音器 громко объявляет 宣布，淡水只在接下来的一个小时内供应。他赶紧装满浴缸和其他容器，以供一天的使用。新德里地方性的短缺很大程度上是因为水务管理者多年前决定将大量上游河流和水库的水 diverted to irrigate crops. 改道用于灌溉农作物。
我的儿子住在干旱的凤凰城，他起床时听到的是洒水器为郊区翠绿的草坪和高尔夫球场浇水的低沉的 schussing 声音。尽管凤凰城坐落在索诺兰沙漠之中，但他却享受着几乎无限的水供应。那里的政治家们允许将灌溉用水从农业 operations 运营转移到城市和郊区，同时允许将 recycled wastewater 再生废水用于景观美化和其他非饮用用途。
正如在新德里和凤凰城一样，世界各地的决策者在如何管理水资源方面 wield great power 拥有巨大的权力。明智地使用这种权力将变得越来越重要，因为随着岁月的流逝，世界对淡水的需求目前正在超过许多地方的 readily supply 现成供应，而且这种情况没有减弱的迹象。这个问题是众所周知的，但这并没有减少它的 disturbing 令人不安的程度：今天，六分之一的人口，超过十亿人，suffering inadequate access to safe freshwater. 遭受无法获得安全淡水的困扰。根据联合国发布的数据，到2025年，全球一半以上国家的淡水资源将 undergo either stress—for example, when people increasingly demand more water than is available or safe for use—or outright shortages. 经历压力——例如，当人们越来越需要比可用或安全使用的水更多的水时——或彻底短缺。到本世纪中叶，地球上多达四分之三的人口可能面临淡水短缺。
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科学家预计水资源短缺将变得更加普遍，这在很大程度上是因为世界人口正在上升，许多人正在变得更富有（从而扩大需求），并且因为全球气候变化正在 exacerbating aridity 加剧干旱并 reducing supply 减少许多地区的供应。更重要的是，许多水源受到 faulty waste disposal, releases of industrial pollutants, fertilizer runoff and coastal influxes of saltwater into aquifers as groundwater is depleted. 有缺陷的废物处理、工业污染物释放、肥料径流以及地下水枯竭时海水涌入含水层的威胁。由于 lack of access to water can lead to starvation, disease, political instability and even armed conflict, failure to take action can have broad and grave consequences. 缺乏用水会导致饥饿、疾病、政治不稳定甚至武装冲突，因此不采取行动可能会产生广泛而严重的后果。
幸运的是，在很大程度上，所需的 technologies and policy tools required to conserve existing freshwater and to secure more of it are known; I will discuss several that seem particularly effective. 用于保护现有淡水和获取更多淡水的技术和政策工具是已知的；我将讨论几种似乎特别有效的方法。现在需要的是行动。各级政府和当局必须 formulate and execute concrete plans for implementing the political, economic and technological measures that can ensure water security now and in the coming decades. 制定并执行具体的计划，以实施政治、经济和技术措施，从而确保现在和未来几十年内的用水安全。
短缺的根源
解决世界水问题首先需要了解每个人需要多少淡水，以及了解阻碍供应和增加世界不同地区需求的因素。斯德哥尔摩国际水研究所的 Malin Falkenmark 和其他专家估计，平均而言，地球上的每个人每年至少需要 1,000 立方米 (m3) 的水——相当于五分之二个奥运会标准游泳池的体积——用于饮用、卫生和种植维持生计的食物。人们是否获得足够的水在很大程度上取决于他们居住的地方，因为全球水资源的 distribution 分布差异很大。
在 drier, underdeveloped and developing nations with large populations 提供充足的水尤其具有挑战性，因为在这些地区需求量大而供应量低。诸如尼罗河、约旦河、长江和恒河等河流不仅 overtaxed 过度使用，而且现在经常在一年中的大部分时间里 peter out 干涸。新德里、北京和许多其他新兴城市地区的地下含水层水位正在下降。
与此同时，淡水短缺在发达国家也变得越来越普遍。例如，美国 recent severe droughts 近期的严重干旱已使佐治亚州北部许多城市和城镇以及西南部大片地区 scrambling for water. 争夺用水。Emblematic of the problem are the man-made lakes Mead and Powell, both of which are fed by the overstressed Colorado River. 这个问题的一个象征是人工湖米德湖和鲍威尔湖，这两个湖泊都由过度使用的科罗拉多河供水。Every year the lakes record their ongoing decline with successive, chalky high-water marks left on their tall canyon walls like so many bathtub rings. 每年，这些湖泊都会记录其持续下降的情况，在它们高耸的峡谷壁上留下连续的、白垩质的高水位线，就像许多浴缸环一样。
黄金法则
当然，location, of course, does not wholly determine the availability of water in a given place: the ability to pay plays a major role. 地理位置当然不能完全决定特定地点的供水情况：支付能力起着重要作用。美国西部的人们有一句老话：“Water usually runs downhill, but it always runs uphill to money.” 水通常向下流，但它总是向上流向金钱。”换句话说，当 supplies are deficient 供应不足时， the powers that be typically divert them to higher-revenue-generating activities at the expense of lower-revenue-generating ones. 当权者通常会将它们转移到更高收入的活动中，而牺牲较低收入的活动。So those with the money get water, while others do not. 因此，有钱人可以得到水，而其他人则没有。
Such arrangements often leave poor people and nonhuman consumers of water—the flora and fauna of the adjacent ecosystems—with insufficient allocations. 这种安排通常会使穷人和非人类用水者——相邻生态系统的动植物——获得不足的分配。And even the best intentions can be distorted by the economic realities described by that Western aphorism. 即使是最好的意图也可能被西方谚语所描述的经济现实所扭曲。
A case in point occurred in one of the best-managed watersheds (or catchments) in the world, the Murray-Darling River Basin in southeast Australia. 一个典型的例子发生在世界上管理最好的流域（或集水区）之一，澳大利亚东南部的墨累-达令河流域。Decades ago the agriculturalists and the government there divided up the waters among the human users—grape growers, wheat farmers and sheep ranchers—in a sophisticated way based on equity and economics. 几十年前，那里的农业学家和政府以一种复杂的方式，基于公平和经济学，在人类用户——葡萄种植者、小麦种植者和绵羊牧场主——之间分配了水资源。The regional water-planning agreement allowed the participants to trade water and market water rights. 区域水资源规划协议允许参与者交易水资源和市场水权。It even reserved a significant part of the aqueous resource for the associated ecosystems and their natural inhabitants, key “users” that are often ignored even though their health in large measure underlies the well-being of their entire region. 它甚至为相关的生态系统及其自然居民保留了 aqueous resource 水资源的重要部分，这些关键的“用户”经常被忽视，即使它们的健康在很大程度上是整个区域福祉的基础。Water and marsh plants, both macro and micro, for example, often do much to remove human-derived waste from the water that passes through the ecosystems in which they live. 例如，水生植物和沼泽植物（无论是大型还是微型）通常在从通过它们生活的生态系统的水中去除人类产生的废物方面做了很多工作。
It turns out, however, that the quantities of water that the planners had set aside to sustain the local environment were inadequate—an underestimation that became apparent during periodic droughts—in particular, the one that has wrought havoc in the area for the last half a dozen years. 然而，事实证明，规划者为维持当地环境而预留的水量是不够的——这种低估在周期性干旱期间变得明显——特别是过去六年中在该地区造成严重破坏的干旱。The territory surrounding the Murray-Darling Basin area dried out and then burned away in tremendous wildfires in recent years. 近年来，墨累-达令河流域周围的 territory 地区干涸，然后在 tremendous wildfires 巨大的野火中烧毁。
The economic actors had all taken their share reasonably enough; they just did not consider the needs of the natural environment, which suffered greatly when its inadequate supply was reduced to critical levels by drought. 经济参与者都合理地分配了他们的份额；他们只是没有考虑到自然环境的需求，当自然环境的不足供应因干旱而减少到 critical levels 临界水平时，自然环境遭受了巨大损失。The members of the Murray-Darling Basin Commission are now frantically trying to extricate themselves from the disastrous results of their misallocation of the total water resource. 墨累-达令河流域委员会的成员现在正在疯狂地试图从他们对水资源总量 misallocation 错误分配造成的灾难性后果中解脱出来。
Given the difficulties of sensibly apportioning the water supply within a single nation, imagine the complexities of doing so for international river basins such as that of the Jordan River, which borders on Lebanon, Syria, Israel, the Palestinian areas and Jordan, all of which have claims to the shared, but limited, supply in an extremely parched region. 考虑到在一个国家内合理分配供水的困难，想象一下为国际河流流域（例如约旦河流域）这样做有多么复杂，约旦河流域与黎巴嫩、叙利亚、以色列、巴勒斯坦地区和约旦接壤，所有这些国家都对这个极度干旱地区共享但有限的供应提出 claim 主张。The struggle for freshwater has contributed to civil and military disputes in the area. 对淡水的争夺导致了该地区的 civil and military disputes 国内和军事争端。Only continuing negotiations and compromise have kept this tense situation under control. 只有持续的谈判和妥协才能使这种紧张局势得到控制。
确定需求
Like supply, demand for water varies from place to place. 与供应一样，对水的需求因地而异。Not only does demand rise with population size and growth rate, it also tends to go up with income level: richer groups generally consume more water, especially in urban and industrial areas. 需求不仅随着人口规模和增长率的上升而上升，而且还往往随着收入水平的提高而上升：富裕群体通常消耗更多的水，尤其是在城市和工业地区。The affluent also insist on services such as wastewater treatment and intensive farm irrigation. 富裕的人还坚持要求诸如 wastewater treatment 废水处理和 intensive farm irrigation 集约化农场灌溉等服务。In many cities, and in particular in the more densely populated territories of Asia and Africa, water demands are growing rapidly. 在许多城市，尤其是在亚洲和非洲人口更稠密的地区，对水的需求正在迅速增长。
In addition to income levels, water prices help to set the extent of demand. 除了收入水平外，水价还有助于确定需求的 extent 程度。For example, in the late 1990s, when my colleagues and I simulated global water use from 2000 until 2050, we found that worldwide water requirements would rise from 3,350 cubic kilometers (km3)—roughly equal to the volume of Lake Huron—to 4,900 km3 if income and prices remained as they were in 1998. 例如，在 1990 年代后期，当我和我的同事模拟了 2000 年至 2050 年的全球用水量时，我们发现，如果收入和价格保持在 1998 年的水平，全球用水需求将从 3,350 立方公里（km 3）——大致相当于休伦湖的体积——增加到 4,900 km 3。（A cubic kilometer of water is equivalent to the volume of 400,000 Olympic swimming pools. 一立方公里的水相当于 40 万个奥运会标准游泳池的体积。）But the demand would grow almost threefold (to 9,250 km3) if the incomes of the poorest nations were to continue to climb to levels equivalent to those of middle-income countries today and if the governments of those nations were to pursue no special policies to restrict water use. 但是，如果最贫穷国家的收入继续攀升至相当于今天中等收入国家水平的水平，并且这些国家的政府不奉行任何限制用水的特殊政策，那么需求将增长近三倍（达到 9,250 km 3）。This increased requirement would greatly intensify the pressure on water supplies, a result that agrees fairly well with forecasts made by the International Water Management Institute (IWMI) when it considered a “business-as-usual,” or “do-nothing-different,” scenario in the 2007 study Water for Food, Water for Life. 这种增加的需求将大大加剧水资源供应的压力，这一结果与国际水管理研究所 (IWMI) 在 2007 年的研究《食品用水，生命之水》中考虑“一切照旧”或“一成不变”的情景时所做的预测相当吻合。
限制浪费的方法
Given the importance of economics and income in water matters, it is clear that reasonable pricing policies that promote greater conservation by domestic and industrial users are worth adopting. 鉴于经济和收入在水事务中的重要性，很明显，值得 adopted 采纳旨在促进家庭和工业用户更大程度节约的合理定价政策。In the past the cost of freshwater in the U.S. and other economic powers has been too low to encourage users to save water: as often happens when people exploit a natural resource, few worry about waste if a commodity is so cheap that it seems almost free. 过去，美国和其他经济强国的淡水成本太低，无法鼓励用户节约用水：正如人们开发自然资源时经常发生的那样，如果一种商品如此便宜以至于似乎几乎免费，那么很少有人担心浪费。
Setting higher prices for water where possible is therefore near the top of my prescription list. 因此，在可能的情况下提高水价几乎是我处方清单的首位。It makes a lot of sense in developed nations, particularly in large cities and industrial areas, and more and more in developing ones as well. 这在发达国家，尤其是在大城市和工业区，以及在越来越多的发展中国家也很有意义。Higher water prices can, for instance, spur the adoption of measures such as the systematic reuse of used water (so-called gray water) for nonpotable applications. 例如，更高的水价可以 spur the adoption of measures 刺激采用诸如系统地重复使用使用过的水（所谓的灰水）用于非饮用用途等措施。It can also encourage water agencies to build recycling and reclamation systems. 它还可以鼓励水务机构建立回收和 reclaimation systems 再生系统。
Raising prices can in addition convince municipalities and others to reduce water losses by improving maintenance of water-delivery systems. 提高价格还可以说服市政当局和其他方面通过改善供水系统的维护来减少水损失。One of the major consequences of pricing water too low is that insufficient funds are generated for future development and preventive upkeep. 对水定价过低的主要后果之一是为 future development 未来发展和 preventive upkeep 预防性维护产生的资金不足。In 2002 the U.S. Government Accountability Office reported that many domestic water utilities defer infrastructure maintenance so that they can remain within their limited operating budgets. 2002 年，美国政府问责办公室报告称，许多国内水务公司推迟基础设施维护，以便它们能够在其有限的运营预算范围内保持运营。Rather than avoiding major failures by detecting leaks early on, they usually wait until water mains break before fixing them. 他们通常不会通过及早发现泄漏来避免重大故障，而是等到水管爆裂才进行修理。
The cost of repairing and modernizing the water infrastructures of the U.S. and Canada to reduce losses and ensure continued operation will be high, however. 然而，修理和现代化美国和加拿大的供水基础设施以减少损失并确保持续运营的成本将很高。The consulting firm Booz Allen Hamilton has projected that the two countries will need to spend $3.6 trillion combined on their water systems over the next 25 years. 咨询公司 Booz Allen Hamilton 预测，这两个国家在未来 25 年内需要在其供水系统上共同花费 3.6 万亿美元。
When the goal is to save water, another key strategy should be to focus on the largest consumers. 当目标是节约用水时，另一个关键策略应该是关注最大的消费者。That approach places irrigated agriculture in the bull’s-eye: compared with any other single activity, conserving irrigation flows would conserve dramatically more freshwater. 这种方法将灌溉农业置于靶心：与其他任何单一活动相比，节约灌溉用水将 dramatically more freshwater 显著节约更多淡水。To meet world food requirements in 2050 without any technological improvements to irrigated agriculture methods, farmers will need a substantial rise in irrigation water supplies (an increase from the current 2,700 to 4,000 km3), according to the IWMI study. 根据 IWMI 的研究，为了在 2050 年满足世界粮食需求，而不在灌溉农业方法上进行任何技术改进，农民将需要 substantial rise in irrigation water supplies 大幅增加灌溉用水供应（从目前的 2,700 km 3 增加到 4,000 km 3）。
On the other hand, even a modest 10 percent rise in irrigation efficiency would free up more water than is evaporated off by all other users. 另一方面，即使灌溉效率 modest 适度提高 10%，释放出的水也比所有其他用户蒸发掉的水还要多。This goal could be achieved by stopping up leaks in the water-delivery infrastructure and by implementing low-loss storage of water as well as more efficient application of water to farm crops. 这个目标可以通过堵住供水基础设施中的泄漏，实施低损耗储水以及更有效地将水用于农作物来实现。
An agreement between municipal water suppliers in southern California and nearby irrigators in the Imperial Irrigation District illustrates one creative conservation effort. 南加州 municipal water suppliers 市政供水商与附近的帝国灌溉区的灌溉者之间的一项协议说明了一项 creative conservation effort 创造性的节约措施。The municipal group is paying to line leaky irrigation canals with waterproof materials, and the water that is saved will go to municipal needs. 市政集团正在出资用防水材料 lining leaky irrigation canals 铺设有漏洞的灌溉渠，节省下来的水将用于满足市政需求。
An additional approach to saving irrigation water involves channeling water that is eventually intended for crop fields to underground storage in the nongrowing season. 另一种节约灌溉用水的方法是在非生长季节将最终 intended for crop fields 用于农田的水 channel to underground storage 输送到地下储存。In most parts of the world, rainfall and snow accumulation—and runoff to rivers—peak during the nongrowing seasons of the year, when demand for irrigation water is lowest. 在世界大部分地区，降雨和积雪——以及流入河流的径流——在一年中的非生长季节达到峰值，此时对灌溉水的需求最低。The fundamental task for managers is therefore to transfer water from the high-supply season to the high-demand season when farmers need to irrigate crops. 因此，管理者 de fundamental task 基本任务是将水从高供应季节转移到农民需要灌溉作物的高需求季节。
The most common solution is to hold surface water behind dams until the growing season, but the exposure evaporates much of this supply. 最常见的解决方案是将地表水蓄积在水坝后面，直到生长季节，但暴露会蒸发掉大部分供应。Underground storage would limit evaporation loss. 地下储存将限制蒸发损失。For such storage to be feasible, engineers would first have to find large subsurface reservoirs that can be recharged readily by surface supplies and that can easily return their contents aboveground when needed for irrigation. 为了使这种储存 feasible 可行，工程师们首先必须找到大型地下水库，这些水库可以很容易地被地表水源 recharge 补给，并且可以在需要灌溉时轻松地将水返回地面。Such “water banks” are currently operating in Arizona, California and elsewhere. 这种“水银行”目前在亚利桑那州、加利福尼亚州和其他地方运营。
More extensive use of drip-irrigation systems, which minimize consumption by allowing water to seep in slowly either from the soil surface or directly into the root zone, would also do much to stem demand for irrigation water. 更广泛地使用 drip-irrigation systems 滴灌系统（通过允许水从土壤表面缓慢渗入或直接渗入根区来最大程度地减少消耗）也将大大有助于 stem demand for irrigation water 抑制对灌溉水的需求。Investments in new crop varieties that can tolerate low water levels and drought, as well as brackish and even saline water, could also help reduce requirements for irrigation water. 对能够 tolerate 耐受低水位和干旱以及微咸水甚至盐水的新作物品种的投资也有助于减少对灌溉水的需求。
Given the rising demand for agricultural products as populations and incomes grow, it is unlikely that water managers can significantly lower the quantity of water now dedicated to irrigated agriculture. 考虑到随着人口和收入的增长，对农产品的需求不断增长，水务管理者不太可能显著降低目前用于灌溉农业的水量。But improvements in irrigation efficiency as well as crop yields can help hold any increases to reasonable levels. 但是，灌溉效率和作物产量的提高可以帮助将任何增长保持在合理水平。
更多要采取的措施
Keeping the demand for irrigation water in arid and semiarid areas down while still meeting the world’s future food requirements can be supported by supplying “virtual water” to those places. 在满足世界未来粮食需求的同时，保持干旱和半干旱地区对灌溉水的 demand down 需求下降可以通过向这些地方供应“虚拟水”来支持。The term relates to the amount of water expended in producing food or commercial goods. 该术语与生产食品或商业 goods 商品所消耗的水量有关。If such products are exported to a dry region, then that area will not have to use its own water to create them. 如果这些产品出口到干旱地区，那么该地区将不必使用自己的水来生产它们。Hence, the items represent a transfer of water to the recipient locale and supply them with so-called virtual water. 因此，这些物品代表了 water transfer 水转移到接收地点，并为它们提供所谓的虚拟水。
The notion of virtual water may sound initially like a mere accounting device, but provision of goods—and the virtual-water content of those goods—is helping many dry countries avoid using their own water supplies for growing crops, thus freeing up large quantities for other applications. 虚拟水的概念最初可能听起来像一个简单的 accounting device 会计工具，但商品的供应——以及这些商品的虚拟水含量——正在帮助许多干旱国家避免使用自己的水资源种植农作物，从而释放大量水用于其他用途。The virtual-water concept and expanded trade have also led to the resolution of many international disputes caused by water scarcity. 虚拟水概念和 expanded trade 扩大的贸易也导致了许多由 water scarcity 缺水引起的国际争端的解决。Imports of virtual water in products by Jordan have reduced the chance of water-based conflict with its neighbor Israel, for example. 例如，约旦产品中虚拟水的进口减少了与其邻国以色列发生水资源冲突的可能性。
The magnitude of annual global trade in virtual water exceeds 800 billion m3 of water a year; the equivalent of 10 Nile Rivers. 全球每年虚拟水贸易的 magnitude 规模超过 8000 亿立方米，相当于 10 条尼罗河。Liberalizing trade of farm products and reducing tariff restrictions that now deter the flow of foodstuffs would significantly enhance global virtual-water flows. 农产品贸易自由化和减少目前 deter the flow of foodstuffs 阻止食品流动的关税限制将显著 enhance global virtual-water flows 增强全球虚拟水流动。Truly free farm trade, for instance, would double the current annual total delivery of virtual water to more than 1.7 trillion m3. 例如，真正的自由农产品贸易将使目前每年虚拟水总交付量翻一番，达到超过 1.7 万亿立方米。
Whatever benefits the world may accrue from virtual-water transfers, the populations of growing cities need real, flowing water to drink, as well as for hygiene and sanitation. 无论世界可能从虚拟水转移中获得何种 benefits 益处，不断增长的城市人口都需要真正的流动水来饮用，以及用于卫生和 sanitation 卫生设施。The ever expanding demand for urban, water-based sanitation services can be reduced by adopting dry, or low-water-use, devices such as dry composting toilets with urine separation systems. 通过采用干燥或低用水量的设备，例如带有尿液分离系统的干式堆肥厕所，可以减少对城市水基卫生服务不断增长的需求。These technologies divert urine for reuse in agriculture and convert the remaining waste on-site into an organic compost that can enrich soil. 这些技术 divert urine 转移尿液以在农业中重复使用，并将剩余的废物在现场转化为可以 enrich soil 肥沃土壤的有机堆肥。Operating basically like garden compost heaps, these units employ aerobic microbes to break down human waste into a nontoxic, nutrient-rich substance. 这些装置基本上像花园堆肥堆一样运行，利用 aerobic microbes 好氧微生物将人类废物分解成无毒、营养丰富的物质。Farmers can exploit the resulting composted organic matter as crop fertilizer. 农民可以 exploit the resulting composted organic matter 利用由此产生的堆肥有机物作为作物肥料。These techniques can be used safely, even in fairly dense urban settings, as exemplified by installations at the Gebers Housing Project in a suburb of Stockholm and many other pilot projects. 这些技术可以安全地使用，即使在相当 dense urban settings 稠密的城市环境中也是如此，斯德哥尔摩郊区的 Gebers 住房项目以及许多其他 pilot projects 试点项目中的装置就是例证。
Essentially, civil engineers can employ this technology to decouple water supplies from sanitation systems, a move that could save significant amounts of freshwater if it were more widely employed. 本质上，土木工程师可以 employ this technology 使用这项技术将供水与卫生系统 decouple 解耦，如果更广泛地使用，这一举措可以节省大量淡水。Moreover, recycled waste could cut the use of fertilizer derived from fossil fuels. 此外，回收的废物可以减少化石燃料 derived from fossil fuels 衍生的肥料的使用。
Beyond constraining demand for freshwater, the opposite approach, increasing its supply, will be a critical component of the solution to water shortages. 除了 constrain demand for freshwater 限制对淡水的需求外，相反的方法，增加其供应，将是解决水资源短缺的关键组成部分。Some 3 percent of all the water on the earth is fresh; all the rest is salty. 地球上约 3% 的水是淡水；其余的都是咸水。But desalination tools are poised to exploit that huge source of salty water. 但是 desalination tools 淡化工具已准备好 exploit that huge source of salty water 开发利用巨大的咸水来源。A recent, substantial reduction in the costs for the most energy-efficient desalination technology—membrane reverse-osmosis systems—means that many coastal cities can now secure new sources of potable water. 最近，最节能的 desalination technology 淡化技术——膜反渗透系统——成本大幅降低，这意味着许多沿海城市现在可以 secure new sources of potable water 获得新的饮用水源。
During reverse osmosis, salty water flows into the first of two chambers that are separated by a semipermeable (water-passing) membrane. 在反渗透过程中，咸水流入由半透膜（透水膜）隔开的两个腔室中的第一个腔室。The second chamber contains freshwater. 第二个腔室包含淡水。Then a substantial amount of pressure is applied to the chamber with the salt solution in it. 然后对装有盐溶液的腔室施加 substantial amount of pressure 大量压力。Over time the pressure forces the water molecules through the membrane to the freshwater side. 随着时间的推移，压力迫使水分子通过膜到达淡水侧。
Engineers have achieved cost savings by implementing a variety of upgrades, including better membranes that require less pressure, and therefore energy, to filter water and system modularization, which makes construction easier. 工程师们通过实施各种 upgrades 升级实现了成本节约，包括需要更少压力（因此也需要更少能量）来过滤水的更好膜，以及使 construction easier 施工更容易的系统 modularization 模块化。Large-scale desalination plants using the new, more economical technology have been built in Singapore and Tampa Bay, Fla. 在新加坡和佛罗里达州坦帕湾已经建造了使用这种新的、更经济技术的大型 desalination plants 淡化厂。
Scientists are now working on reverse-osmosis filters composed of carbon nanotubes that offer better separation efficiencies and the potential of lowering desalination costs by an additional 30 percent. 科学家们现在正在研究由碳纳米管组成的反渗透过滤器，这种过滤器具有更好的分离效率，并有可能将 desalination costs 淡化成本再降低 30%。This technology, which has been demonstrated in prototypes, is steadily approaching commercial use. 这项技术已在 prototypes 原型中得到 demonstration 演示，正在稳步接近 commercial use 商业用途。Despite the improvements in energy efficiency, however, the applicability of reverse osmosis is to some degree limited by the fact that the technology is still energy-intensive, so the availability of affordable power is important to significantly expanding its application. 尽管能源效率有所提高，但反渗透的 applicability 适用性在某种程度上受到限制，因为该技术仍然是 energy-intensive 高能耗的，因此 affordable power 负担得起的电力供应对于显著扩大其应用非常重要。
投资回报
Not surprisingly, staving off future water shortages means spending money—a lot of it. 毫不奇怪，staving off future water shortages 避免未来水资源短缺意味着花钱——很多钱。Analysts at Booz Allen Hamilton have estimated that to provide water needed for all uses through 2030, the world will need to invest as much as $1 trillion a year on applying existing technologies for conserving water, maintaining and replacing infrastructure, and constructing sanitation systems. Booz Allen Hamilton 的分析师估计，为了提供到 2030 年所有用途所需的水，世界每年需要投资多达 1 万亿美元，用于应用现有技术来节约用水、维护和更换基础设施以及建设卫生系统。This is a daunting figure to be sure, but perhaps not so huge when put in perspective. 这肯定是一个 daunting figure 令人胆寒的数字，但如果放在 perspective 角度来看，也许并没有那么巨大。The required sum turns out to be about 1.5 percent of today’s annual global gross domestic product, or about $120 per capita, a seemingly achievable expenditure. 所需的金额结果约为当今全球年 gross domestic product 国内生产总值的 1.5%，或约人均 120 美元，这似乎是一项 achievable expenditure 可实现的支出。
Unfortunately, investment in water facilities as a percentage of gross domestic product has dropped by half in most countries since the late 1990s. 不幸的是，自 1990 年代后期以来，大多数国家对水设施的投资占国内生产总值的百分比下降了一半。If a crisis arises in the coming decades, it will not be for lack of know-how; it will come from a lack of foresight and from an unwillingness to spend the needed money. 如果危机在未来几十年内爆发，那将不是因为缺乏 know-how 专业知识；而是因为缺乏 foresight 远见卓识和不愿意花必要的钱。
There is, however, at least one cause for optimism: the most populous countries with the largest water infrastructure needs—India and China—are precisely those that are experiencing rapid economic growth. 然而，至少有一个乐观的理由：人口最多、对水基础设施需求最大的国家——印度和中国——恰恰是那些正在经历 rapid economic growth 快速经济增长的国家。The part of the globe that is most likely to continue suffering from inadequate water access—Africa and its one billion inhabitants—spends the least on water infrastructure and cannot afford to spend much; it is crucial, therefore, that wealthier nations provide more funds to assist the effort. 最有可能继续 suffering from inadequate water access 遭受无法获得足够用水困扰的全球地区——非洲及其十亿居民——在水基础设施上的花费最少，并且负担不起太多花费；因此，wealthier nations 富裕国家提供更多资金来协助这项工作至关重要。
The international community can reduce the chances of a global water crisis if it puts its collective mind to the challenge. 如果国际社会将其 collective mind 集体智慧投入到挑战中，就可以减少全球水危机的机会。We do not have to invent new technologies; we must simply accelerate the adoption of existing techniques to conserve and enhance the water supply. 我们不必发明新技术；我们必须简单地 accelerate the adoption of existing techniques 加快采用现有技术来节约和增加供水。Solving the water problem will not be easy, but we can succeed if we start right away and stick to it. 解决水问题并非易事，但如果我们立即开始并坚持下去，我们就能成功。Otherwise, much of the world will go thirsty. 否则，世界上大部分地区都会口渴。
