我的一個朋友住在印度最富裕的城市之一新德里一箇中產階級社群。儘管該地區每年有相當多的降雨，但他早上醒來時卻聽到擴音器 громко объявляет 宣佈，淡水只在接下來的一個小時內供應。他趕緊裝滿浴缸和其他容器，以供一天的使用。新德里地方性的短缺很大程度上是因為水務管理者多年前決定將大量上游河流和水庫的水 diverted to irrigate crops. 改道用於灌溉農作物。
我的兒子住在乾旱的鳳凰城，他起床時聽到的是灑水器為郊區翠綠的草坪和高爾夫球場澆水的低沉的 schussing 聲音。儘管鳳凰城坐落在索諾蘭沙漠之中，但他卻享受著幾乎無限的水供應。那裡的政治家們允許將灌溉用水從農業 operations 運營轉移到城市和郊區，同時允許將 recycled wastewater 再生廢水用於景觀美化和其他非飲用用途。
正如在新德里和鳳凰城一樣，世界各地的決策者在如何管理水資源方面 wield great power 擁有巨大的權力。明智地使用這種權力將變得越來越重要，因為隨著歲月的流逝，世界對淡水的需求目前正在超過許多地方的 readily supply 現成供應，而且這種情況沒有減弱的跡象。這個問題是眾所周知的，但這並沒有減少它的 disturbing 令人不安的程度：今天，六分之一的人口，超過十億人，suffering inadequate access to safe freshwater. 遭受無法獲得安全淡水的困擾。根據聯合國釋出的資料，到2025年，全球一半以上國家的淡水資源將 undergo either stress—for example, when people increasingly demand more water than is available or safe for use—or outright shortages. 經歷壓力——例如，當人們越來越需要比可用或安全使用的水更多的水時——或徹底短缺。到本世紀中葉，地球上多達四分之三的人口可能面臨淡水短缺。
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科學家預計水資源短缺將變得更加普遍，這在很大程度上是因為世界人口正在上升，許多人正在變得更富有（從而擴大需求），並且因為全球氣候變化正在 exacerbating aridity 加劇乾旱並 reducing supply 減少許多地區的供應。更重要的是，許多水源受到 faulty waste disposal, releases of industrial pollutants, fertilizer runoff and coastal influxes of saltwater into aquifers as groundwater is depleted. 有缺陷的廢物處理、工業汙染物釋放、肥料徑流以及地下水枯竭時海水湧入含水層的威脅。由於 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. 缺乏用水會導致飢餓、疾病、政治不穩定甚至武裝衝突，因此不採取行動可能會產生廣泛而嚴重的後果。
幸運的是，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. 用於保護現有淡水和獲取更多淡水的技術和政策工具是已知的；我將討論幾種似乎特別有效的方法。現在需要的是行動。各級政府和當局必須 formulate and execute concrete plans for implementing the political, economic and technological measures that can ensure water security now and in the coming decades. 制定並執行具體的計劃，以實施政治、經濟和技術措施，從而確保現在和未來幾十年內的用水安全。
短缺的根源
解決世界水問題首先需要了解每個人需要多少淡水，以及瞭解阻礙供應和增加世界不同地區需求的因素。斯德哥爾摩國際水研究所的 Malin Falkenmark 和其他專家估計，平均而言，地球上的每個人每年至少需要 1,000 立方米 (m3) 的水——相當於五分之二個奧運會標準游泳池的體積——用於飲用、衛生和種植維持生計的食物。人們是否獲得足夠的水在很大程度上取決於他們居住的地方，因為全球水資源的 distribution 分佈差異很大。
在 drier, underdeveloped and developing nations with large populations 提供充足的水尤其具有挑戰性，因為在這些地區需求量大而供應量低。諸如尼羅河、約旦河、長江和恆河等河流不僅 overtaxed 過度使用，而且現在經常在一年中的大部分時間裡 peter out 乾涸。新德里、北京和許多其他新興城市地區的地下含水層水位正在下降。
與此同時，淡水短缺在發達國家也變得越來越普遍。例如，美國 recent severe droughts 近期的嚴重乾旱已使佐治亞州北部許多城市和城鎮以及西南部大片地區 scrambling for water. 爭奪用水。Emblematic of the problem are the man-made lakes Mead and Powell, both of which are fed by the overstressed Colorado River. 這個問題的一個象徵是人工湖米德湖和鮑威爾湖，這兩個湖泊都由過度使用的科羅拉多河供水。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，這些湖泊都會記錄其持續下降的情況，在它們高聳的峽谷壁上留下連續的、白堊質的高水位線，就像許多浴缸環一樣。
黃金法則
當然，location, of course, does not wholly determine the availability of water in a given place: the ability to pay plays a major role. 地理位置當然不能完全決定特定地點的供水情況：支付能力起著重要作用。美國西部的人們有一句老話：“Water usually runs downhill, but it always runs uphill to money.” 水通常向下流，但它總是向上流向金錢。”換句話說，當 supplies are deficient 供應不足時， the powers that be typically divert them to higher-revenue-generating activities at the expense of lower-revenue-generating ones. 當權者通常會將它們轉移到更高收入的活動中，而犧牲較低收入的活動。So those with the money get water, while others do not. 因此，有錢人可以得到水，而其他人則沒有。
Such arrangements often leave poor people and nonhuman consumers of water—the flora and fauna of the adjacent ecosystems—with insufficient allocations. 這種安排通常會使窮人和非人類用水者——相鄰生態系統的動植物——獲得不足的分配。And even the best intentions can be distorted by the economic realities described by that Western aphorism. 即使是最好的意圖也可能被西方諺語所描述的經濟現實所扭曲。
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. 一個典型的例子發生在世界上管理最好的流域（或集水區）之一，澳大利亞東南部的墨累-達令河流域。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. 幾十年前，那裡的農業學家和政府以一種複雜的方式，基於公平和經濟學，在人類使用者——葡萄種植者、小麥種植者和綿羊牧場主——之間分配了水資源。The regional water-planning agreement allowed the participants to trade water and market water rights. 區域水資源規劃協議允許參與者交易水資源和市場水權。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. 它甚至為相關的生態系統及其自然居民保留了 aqueous resource 水資源的重要部分，這些關鍵的“使用者”經常被忽視，即使它們的健康在很大程度上是整個區域福祉的基礎。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，水生植物和沼澤植物（無論是大型還是微型）通常在從透過它們生活的生態系統的水中去除人類產生的廢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，事實證明，規劃者為維持當地環境而預留的水量是不夠的——這種低估在週期性乾旱期間變得明顯——特別是過去六年中在該地區造成嚴重破壞的乾旱。The territory surrounding the Murray-Darling Basin area dried out and then burned away in tremendous wildfires in recent years. 近年來，墨累-達令河流域周圍的 territory 地區乾涸，然後在 tremendous wildfires 巨大的野火中燒燬。
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. 經濟參與者都合理地分配了他們的份額；他們只是沒有考慮到自然環境的需求，當自然環境的不足供應因乾旱而減少到 critical levels 臨界水平時，自然環境遭受了巨大損失。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-達令河流域委員會的成員現在正在瘋狂地試圖從他們對水資源總量 misallocation 錯誤分配造成的災難性後果中解脫出來。
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. 考慮到在一個國家內合理分配供水的困難，想象一下為國際河流流域（例如約旦河流域）這樣做有多麼複雜，約旦河流域與黎巴嫩、敘利亞、以色列、巴勒斯坦地區和約旦接壤，所有這些國家都對這個極度乾旱地區共享但有限的供應提出 claim 主張。The struggle for freshwater has contributed to civil and military disputes in the area. 對淡水的爭奪導致了該地區的 civil and military disputes 國內和軍事爭端。Only continuing negotiations and compromise have kept this tense situation under control. 只有持續的談判和妥協才能使這種緊張局勢得到控制。
確定需求
Like supply, demand for water varies from place to place. 與供應一樣，對水的需求因地而異。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. 需求不僅隨著人口規模和增長率的上升而上升，而且還往往隨著收入水平的提高而上升：富裕群體通常消耗更多的水，尤其是在城市和工業地區。The affluent also insist on services such as wastewater treatment and intensive farm irrigation. 富裕的人還堅持要求諸如 wastewater treatment 廢水處理和 intensive farm irrigation 集約化農場灌溉等服務。In many cities, and in particular in the more densely populated territories of Asia and Africa, water demands are growing rapidly. 在許多城市，尤其是在亞洲和非洲人口更稠密的地區，對水的需求正在迅速增長。
In addition to income levels, water prices help to set the extent of demand. 除了收入水平外，水價還有助於確定需求的 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 年代後期，當我和我的同事模擬了 2000 年至 2050 年的全球用水量時，我們發現，如果收入和價格保持在 1998 年的水平，全球用水需求將從 3,350 立方公里（km 3）——大致相當於休倫湖的體積——增加到 4,900 km 3。（A cubic kilometer of water is equivalent to the volume of 400,000 Olympic swimming pools. 一立方公里的水相當於 40 萬個奧運會標準游泳池的體積。）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，如果最貧窮國家的收入繼續攀升至相當於今天中等收入國家水平的水平，並且這些國家的政府不奉行任何限制用水的特殊政策，那麼需求將增長近三倍（達到 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. 這種增加的需求將大大加劇水資源供應的壓力，這一結果與國際水管理研究所 (IWMI) 在 2007 年的研究《食品用水，生命之水》中考慮“一切照舊”或“一成不變”的情景時所做的預測相當吻合。
限制浪費的方法
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. 鑑於經濟和收入在水事務中的重要性，很明顯，值得 adopted 採納旨在促進家庭和工業使用者更大程度節約的合理定價政策。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. 過去，美國和其他經濟強國的淡水成本太低，無法鼓勵使用者節約用水：正如人們開發自然資源時經常發生的那樣，如果一種商品如此便宜以至於似乎幾乎免費，那麼很少有人擔心浪費。
Setting higher prices for water where possible is therefore near the top of my prescription list. 因此，在可能的情況下提高水價幾乎是我處方清單的首位。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. 這在發達國家，尤其是在大城市和工業區，以及在越來越多的發展中國家也很有意義。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，更高的水價可以 spur the adoption of measures 刺激採用諸如系統地重複使用使用過的水（所謂的灰水）用於非飲用用途等措施。It can also encourage water agencies to build recycling and reclamation systems. 它還可以鼓勵水務機構建立回收和 reclaimation systems 再生系統。
Raising prices can in addition convince municipalities and others to reduce water losses by improving maintenance of water-delivery systems. 提高價格還可以說服市政當局和其他方面透過改善供水系統的維護來減少水損失。One of the major consequences of pricing water too low is that insufficient funds are generated for future development and preventive upkeep. 對水定價過低的主要後果之一是為 future development 未來發展和 preventive upkeep 預防性維護產生的資金不足。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，美國政府問責辦公室報告稱，許多國內水務公司推遲基礎設施維護，以便它們能夠在其有限的運營預算範圍內保持運營。Rather than avoiding major failures by detecting leaks early on, they usually wait until water mains break before fixing them. 他們通常不會透過及早發現洩漏來避免重大故障，而是等到水管爆裂才進行修理。
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，修理和現代化美國和加拿大的供水基礎設施以減少損失並確保持續運營的成本將很高。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. 諮詢公司 Booz Allen Hamilton 預測，這兩個國家在未來 25 年內需要在其供水系統上共同花費 3.6 萬億美元。
When the goal is to save water, another key strategy should be to focus on the largest consumers. 當目標是節約用水時，另一個關鍵策略應該是關注最大的消費者。That approach places irrigated agriculture in the bull’s-eye: compared with any other single activity, conserving irrigation flows would conserve dramatically more freshwater. 這種方法將灌溉農業置於靶心：與其他任何單一活動相比，節約灌溉用水將 dramatically more freshwater 顯著節約更多淡水。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. 根據 IWMI 的研究，為了在 2050 年滿足世界糧食需求，而不在灌溉農業方法上進行任何技術改進，農民將需要 substantial rise in irrigation water supplies 大幅增加灌溉用水供應（從目前的 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 適度提高 10%，釋放出的水也比所有其他使用者蒸發掉的水還要多。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. 這個目標可以透過堵住供水基礎設施中的洩漏，實施低損耗儲水以及更有效地將水用於農作物來實現。
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 市政供水商與附近的帝國灌溉區的灌溉者之間的一項協議說明了一項 creative conservation effort 創造性的節約措施。The municipal group is paying to line leaky irrigation canals with waterproof materials, and the water that is saved will go to municipal needs. 市政集團正在出資用防水材料 lining leaky irrigation canals 鋪設有漏洞的灌溉渠，節省下來的水將用於滿足市政需求。
An additional approach to saving irrigation water involves channeling water that is eventually intended for crop fields to underground storage in the nongrowing season. 另一種節約灌溉用水的方法是在非生長季節將最終 intended for crop fields 用於農田的水 channel to underground storage 輸送到地下儲存。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. 在世界大部分地區，降雨和積雪——以及流入河流的徑流——在一年中的非生長季節達到峰值，此時對灌溉水的需求最低。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 基本任務是將水從高供應季節轉移到農民需要灌溉作物的高需求季節。
The most common solution is to hold surface water behind dams until the growing season, but the exposure evaporates much of this supply. 最常見的解決方案是將地表水蓄積在水壩後面，直到生長季節，但暴露會蒸發掉大部分供應。Underground storage would limit evaporation loss. 地下儲存將限制蒸發損失。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. 為了使這種儲存 feasible 可行，工程師們首先必須找到大型地下水庫，這些水庫可以很容易地被地表水源 recharge 補給，並且可以在需要灌溉時輕鬆地將水返回地面。Such “water banks” are currently operating in Arizona, California and elsewhere. 這種“水銀行”目前在亞利桑那州、加利福尼亞州和其他地方運營。
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. 更廣泛地使用 drip-irrigation systems 滴灌系統（透過允許水從土壤表面緩慢滲入或直接滲入根區來最大程度地減少消耗）也將大大有助於 stem demand for irrigation water 抑制對灌溉水的需求。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. 對能夠 tolerate 耐受低水位和乾旱以及微鹹水甚至鹽水的新作物品種的投資也有助於減少對灌溉水的需求。
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. 考慮到隨著人口和收入的增長，對農產品的需求不斷增長，水務管理者不太可能顯著降低目前用於灌溉農業的水量。But improvements in irrigation efficiency as well as crop yields can help hold any increases to reasonable levels. 但是，灌溉效率和作物產量的提高可以幫助將任何增長保持在合理水平。
更多要採取的措施
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. 在滿足世界未來糧食需求的同時，保持乾旱和半乾旱地區對灌溉水的 demand down 需求下降可以透過向這些地方供應“虛擬水”來支援。The term relates to the amount of water expended in producing food or commercial goods. 該術語與生產食品或商業 goods 商品所消耗的水量有關。If such products are exported to a dry region, then that area will not have to use its own water to create them. 如果這些產品出口到乾旱地區，那麼該地區將不必使用自己的水來生產它們。Hence, the items represent a transfer of water to the recipient locale and supply them with so-called virtual water. 因此，這些物品代表了 water transfer 水轉移到接收地點，併為它們提供所謂的虛擬水。
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. 虛擬水的概念最初可能聽起來像一個簡單的 accounting device 會計工具，但商品的供應——以及這些商品的虛擬水含量——正在幫助許多幹旱國家避免使用自己的水資源種植農作物，從而釋放大量水用於其他用途。The virtual-water concept and expanded trade have also led to the resolution of many international disputes caused by water scarcity. 虛擬水概念和 expanded trade 擴大的貿易也導致了許多由 water scarcity 缺水引起的國際爭端的解決。Imports of virtual water in products by Jordan have reduced the chance of water-based conflict with its neighbor Israel, for example. 例如，約旦產品中虛擬水的進口減少了與其鄰國以色列發生水資源衝突的可能性。
The magnitude of annual global trade in virtual water exceeds 800 billion m3 of water a year; the equivalent of 10 Nile Rivers. 全球每年虛擬水貿易的 magnitude 規模超過 8000 億立方米，相當於 10 條尼羅河。Liberalizing trade of farm products and reducing tariff restrictions that now deter the flow of foodstuffs would significantly enhance global virtual-water flows. 農產品貿易自由化和減少目前 deter the flow of foodstuffs 阻止食品流動的關稅限制將顯著 enhance global virtual-water flows 增強全球虛擬水流動。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，真正的自由農產品貿易將使目前每年虛擬水總交付量翻一番，達到超過 1.7 萬億立方米。
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. 無論世界可能從虛擬水轉移中獲得何種 benefits 益處，不斷增長的城市人口都需要真正的流動水來飲用，以及用於衛生和 sanitation 衛生設施。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. 透過採用乾燥或低用水量的裝置，例如帶有尿液分離系統的乾式堆肥廁所，可以減少對城市水基衛生服務不斷增長的需求。These technologies divert urine for reuse in agriculture and convert the remaining waste on-site into an organic compost that can enrich soil. 這些技術 divert urine 轉移尿液以在農業中重複使用，並將剩餘的廢物在現場轉化為可以 enrich soil 肥沃土壤的有機堆肥。Operating basically like garden compost heaps, these units employ aerobic microbes to break down human waste into a nontoxic, nutrient-rich substance. 這些裝置基本上像花園堆肥堆一樣執行，利用 aerobic microbes 好氧微生物將人類廢物分解成無毒、營養豐富的物質。Farmers can exploit the resulting composted organic matter as crop fertilizer. 農民可以 exploit the resulting composted organic matter 利用由此產生的堆肥有機物作為作物肥料。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. 這些技術可以安全地使用，即使在相當 dense urban settings 稠密的城市環境中也是如此，斯德哥爾摩郊區的 Gebers 住房專案以及許多其他 pilot projects 試點專案中的裝置就是例證。
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. 本質上，土木工程師可以 employ this technology 使用這項技術將供水與衛生系統 decouple 解耦，如果更廣泛地使用，這一舉措可以節省大量淡水。Moreover, recycled waste could cut the use of fertilizer derived from fossil fuels. 此外，回收的廢物可以減少化石燃料 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 限制對淡水的需求外，相反的方法，增加其供應，將是解決水資源短缺的關鍵組成部分。Some 3 percent of all the water on the earth is fresh; all the rest is salty. 地球上約 3% 的水是淡水；其餘的都是鹹水。But desalination tools are poised to exploit that huge source of salty water. 但是 desalination tools 淡化工具已準備好 exploit that huge source of salty water 開發利用巨大的鹹水來源。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，最節能的 desalination technology 淡化技術——膜反滲透系統——成本大幅降低，這意味著許多沿海城市現在可以 secure new sources of potable water 獲得新的飲用水源。
During reverse osmosis, salty water flows into the first of two chambers that are separated by a semipermeable (water-passing) membrane. 在反滲透過程中，鹹水流入由半透膜（透水膜）隔開的兩個腔室中的第一個腔室。The second chamber contains freshwater. 第二個腔室包含淡水。Then a substantial amount of pressure is applied to the chamber with the salt solution in it. 然後對裝有鹽溶液的腔室施加 substantial amount of pressure 大量壓力。Over time the pressure forces the water molecules through the membrane to the freshwater side. 隨著時間的推移，壓力迫使水分子透過膜到達淡水側。
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. 工程師們透過實施各種 upgrades 升級實現了成本節約，包括需要更少壓力（因此也需要更少能量）來過濾水的更好膜，以及使 construction easier 施工更容易的系統 modularization 模組化。Large-scale desalination plants using the new, more economical technology have been built in Singapore and Tampa Bay, Fla. 在新加坡和佛羅里達州坦帕灣已經建造了使用這種新的、更經濟技術的大型 desalination plants 淡化廠。
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. 科學家們現在正在研究由碳奈米管組成的反滲透過濾器，這種過濾器具有更好的分離效率，並有可能將 desalination costs 淡化成本再降低 30%。This technology, which has been demonstrated in prototypes, is steadily approaching commercial use. 這項技術已在 prototypes 原型中得到 demonstration 演示，正在穩步接近 commercial use 商業用途。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. 儘管能源效率有所提高，但反滲透的 applicability 適用性在某種程度上受到限制，因為該技術仍然是 energy-intensive 高能耗的，因此 affordable power 負擔得起的電力供應對於顯著擴大其應用非常重要。
投資回報
Not surprisingly, staving off future water shortages means spending money—a lot of it. 毫不奇怪，staving off future water shortages 避免未來水資源短缺意味著花錢——很多錢。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 的分析師估計，為了提供到 2030 年所有用途所需的水，世界每年需要投資多達 1 萬億美元，用於應用現有技術來節約用水、維護和更換基礎設施以及建設衛生系統。This is a daunting figure to be sure, but perhaps not so huge when put in perspective. 這肯定是一個 daunting figure 令人膽寒的數字，但如果放在 perspective 角度來看，也許並沒有那麼巨大。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. 所需的金額結果約為當今全球年 gross domestic product 國內生產總值的 1.5%，或約人均 120 美元，這似乎是一項 achievable expenditure 可實現的支出。
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 年代後期以來，大多數國家對水設施的投資佔國內生產總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. 如果危機在未來幾十年內爆發，那將不是因為缺乏 know-how 專業知識；而是因為缺乏 foresight 遠見卓識和不願意花必要的錢。
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，至少有一個樂觀的理由：人口最多、對水基礎設施需求最大的國家——印度和中國——恰恰是那些正在經歷 rapid economic growth 快速經濟增長的國家。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. 最有可能繼續 suffering from inadequate water access 遭受無法獲得足夠用水困擾的全球地區——非洲及其十億居民——在水基礎設施上的花費最少，並且負擔不起太多花費；因此，wealthier nations 富裕國家提供更多資金來協助這項工作至關重要。
The international community can reduce the chances of a global water crisis if it puts its collective mind to the challenge. 如果國際社會將其 collective mind 集體智慧投入到挑戰中，就可以減少全球水危機的機會。We do not have to invent new technologies; we must simply accelerate the adoption of existing techniques to conserve and enhance the water supply. 我們不必發明新技術；我們必須簡單地 accelerate the adoption of existing techniques 加快採用現有技術來節約和增加供水。Solving the water problem will not be easy, but we can succeed if we start right away and stick to it. 解決水問題並非易事，但如果我們立即開始並堅持下去，我們就能成功。Otherwise, much of the world will go thirsty. 否則，世界上大部分地區都會口渴。
