水的用途通常分为三类：农业用水、工业用水和市政用水，市政用水包括家庭饮水。近年来，人们日益重视水的第四类用途，即自然生态系统、包括河流、湖泊和湿地对水的需求，它们提供了养鱼场、生物多样性、水的净化、运输和娱乐等宝贵的经济和社会服务。在全球范围，抽取的地下水中大约有三分之二用于农业，三分之一左右用于工业，10%左右用于市政用途。大部分农业用水供作物消费或者被蒸发，几乎所有工业用水和家庭用水在使用后又回到水体之中，这些水常常受到污染。为发电、蓄水和防洪而建设的水坝和水库都是暂时性储存水，对水的其他用途产生影响。
水资源综合管理涉及将水分配给这些相互竞争的用途以及各部门中的不同用户，促进生产性和高效率用水以及保护水质，目的是促进经济长期增长、社会发展和环境保护。《约翰内斯堡执行计划》呼吁在2005年底之前制订水资源综合管理和用水效率计划。虽然有迹象表明许多国家正在努力处理这些问题，但是，尚没有足够的标准或信息来评估实现这项指标的进展情况。
在发展中国家，70%～90%的水用于农业，灌溉用水资源的发展是近几十年来人均粮食生产增长的重要因素。预计2000年～2030年期间，农业用水将增加约14%，低于以往的增长速度，也低于人口增长率。由于最容易利用的水源已经开发，增加农业用水将变得愈加困难，现在人们更加关注水坝所产生的社会和环境影响。因此，农业生产的进一步增长将更多地取决于能否在土地和水这两方面提高农业生产率。
在许多发展中国家，平均灌溉效率依然很低，菲律宾、泰国、印度、巴基斯坦和墨西哥为25％～40%，马来西亚和摩洛哥为40％～45%。以色列和日本的平均数字为50％～60%。农业用水即使略有节约也可以在很大程度上满足数量较少但日益增长的工业或家庭用水需求。譬如，也门阿比扬--图班三角洲的灌溉效率如果从45%提高到60%，每年就可以在目前的漫灌用水中节省6500万立方米地表水。在许多国家，对灌溉用水的巨额补贴继续破坏为提高水的效率而作出的努力。
但是，由于开展机构改革和政策改革，有更多预防性研究和推广系统在推广高效率用水管理办法，以及改善灌溉技术，因此，农业用水的生产率普遍得到提高。目前存在很大潜力，可以采用各种办法进一步提高农业用水的生产率，例如减少灌溉系统所损失的水，改善农场用水管理办法，实施需求管理措施，改善基础设施的运营和维修以及改种用水较少的作物。许多国家正在努力提高农业用水的生产率。譬如，南非政治改革之后，在水务部门的改革中将农业用水需求管理列为优先目标。在印度尼西亚，水务管理主要是提高农业生产率和改善灌溉的效能，方法是开展参与性管理，建立和加强水用户协会，以及协助农民获得农业技术服务和微额贷款。现在许多地区，特别是在亚洲和北非，最严峻的挑战依然是如何改造灌溉渠道，开垦涝地和盐碱地，通过疏浚恢复水库已经丧失的储水能力。
越来越多的国家将地方灌溉分支系统的管理责任移交给使用这种分支系统的农民，政府通常保留基础设施的所有权以及对灌溉干道系统的管理责任。在大多数情况下，这种管理的转让降低了运营和维修成本，改善了收费情况，提高了用水效率，用户之间的分配量更加公平。比如，在墨西哥，政府将灌溉系统的管理责任转交给用户协会之后，运营和维修成本的回收率从30%提高到80%。
南亚各国实施了广泛的灌溉改良方案，从加固沟渠干道到合作管理共享的水道。但是，由于缺乏大量资本而影响了进展。农民借款和偿付能力有限，因此采用先进的节水技术速度较慢，而施政机制不完备也阻碍了推广这些技术的信贷方案。
在许多国家，管理需求的措施在养护水资源方面取得了成功。发达国家和发展中国家都减少了对灌溉用水的补贴并提高了成本回收率，以期改善供水筹资和提高效率。
尽管各国努力提高灌溉用水的效率，但人们常常将匮乏的水源用于用水量高、价值低的生产，妨碍了将水用于能促进经济和社会发展的用途。但是，许多国家的经验表明很难改变水的分配量。各国政府在考虑灌溉项目提案时，往往不能在水资源综合管理的框架内充分考虑经济、环境和社会的可持续性。
在许多地区，尤其在亚洲，灌溉管理不良导致土地退化，降低了生产率，甚至造成土地完全不适用于农业。在全球范围内，大约2000万～3000万公顷灌溉土地已经严重盐碱化，另有6000万～8000万公顷土地因积水和盐碱化已在一定程度上退化。澳大利亚默累-达令流域是采取有效的物资和需求管理措施处理土地和水资源退化的一个实例。另一个实例是尼罗河流域各国正在捐赠者的协调资助下制订“共同远景方案”，以期建立一个执行水资源管理项目的协调机制和有利的环境。另一方面，西非尼罗河流域所规划的举措推迟执行，进一步破坏了生态系统，并且威胁着许多贫穷的农村经济体的可持续性。
许多小岛屿发展中国家和沿海地区面临的一个问题是，在大多数人口居住的沿海地区含水层抽出淡水时，盐水会侵入。在这些地区，例如在马绍尔群岛，利用简单的“清除式水井”技术从深层盐水上方很薄的淡水层中抽水，取得了良好的成果，但是由于资金限制，采用这种技术速度很缓慢。
在水力发电方面，发展中国家的大部分潜力未得到利用。譬如，撒哈拉以南非洲和中亚仅利用了17%的经济水力发电潜力，亚太区域仅发挥大约29%的潜力，而发挥的技术潜力就更少。造成这种现象的部分原因是新资源地点和电力需求往往不相符合，其他限制原因是需要巨额资本以及对环境和社会的影响。在国际水道上建立水坝的位置也会造成国际关系进一步复杂化。
大多数发展中国家正在促进本国工业部门的发展，这往往会加剧水污染问题。环境条例(包括排污标准)跟不上工业发展的速度。许多发展中国家的水务施政和条例实施机制薄弱，限制了工业部门在清洁的生产技术和废水处理方面投资的积极性。虽然发展中国家在这方面与目前发达国家在工业化时期的情况没有差异，但是，它们可以受益于那一时期所取得的技术进步，这种技术进步提高了使用生产投入的效率，减少了废料，从而也减少排放到水和其他介质中的废料。
国际江河流域的可持续发展对于可持续发展具有重要意义。仅非洲就有59条国际江河流域，占非洲大陆地表水资源的80%。国际法在改善沿岸国合作方面没有取得很大进展。许多与水有关的长期争端没有得到解决，对有限的淡水资源的需求不断增长，加剧了今后发生冲突的危险。在经合组织国家中，综合处理跨界水域沿岸上游和下游利益的问题日益得到重视。在发展中国家，湄公河委员会是沿岸国开展合作与协调的一种长期机制，但由于缺乏重要的上游沿岸国，限制了该组织的效能。在过去10年中，尼罗河流域国家提出了一项关于有效管理和使用资源的共同远景。
原文如下：
Water management
Water use has conventionally been considered in three categories: agricultural use, industrial use, and municipal use, which includes household drinking water. In recent years, increasing attention has been paid to a fourth category, the water requirements of natural ecosystems including rivers, lakes and wetlands, which provide valuable economic and social services such as fisheries, biodiversity, water purification, transportation and recreation. Globally, about two thirds of extractive water usage is for agriculture, about one quarter for industry, and about 10 per cent for municipal use. Most water used for agriculture is consumed by crops or lost to evaporation, while almost all the water used by industry and households is returned to water bodies after use, though often in polluted form. Dams and reservoirs for hydropower, water storage and flood control store water temporarily, affecting other uses of water.
Integrated water-resources management involves allocation of water among those competing uses, and among users within each sector, promoting productive and efficient use of the water, and protecting water quality, so as to promote long- term economic growth, social development and environmental protection. The Johannesburg Plan of Implementation calls for the development of integrated waterresources management and water-efficiency plans by 2005. While there are indications that many countries are working on those issues, there are no adequate criteria or information to assess progress towards the target.
In developing countries, most water - 70 per cent to 90 per cent - is used for agriculture, and the development of water resources for irrigation has been a major factor in the growth in food production per capita in recent decades. Agricultural water use is expected to increase by about 14 per cent between 2000 and 2030, a slower rate than in the past, and slower than population growth. Increasing water supplies for irrigation will be more difficult as the easiest sources have already been developed, and there are now greater concerns over the social and environmental impacts of dams. Further growth in agricultural production will therefore depend more on increasing agricultural productivity with respect to both land and water.
Average irrigation efficiency remains low in many developing countries, ranging from 25-40 per cent for the Philippines, Thailand, India, Pakistan and Mexico, to 40-45 per cent in Malaysia and Morocco. Those figures are below what can be achieved; average figures for Israel and Japan, for example, range from 50-60 per cent. Even modest savings in agricultural water use could contribute substantially to meeting the smaller but growing water demands for industrial or household use. For example, an improvement in irrigation efficiency in the Abyan- Tuban delta of Yemen from 45 per cent to 60 per cent could result in an annual saving of 65 million cubic metres of surface water that is at present used in spate irrigation.21 In many countries, large subsidies of irrigation water continue to undermine efforts to improve water efficiency.
Still, water productivity in agriculture has generally been improving as a result of institutional and policy reforms, more proactive research and extension systems promoting efficient water-management practices, and improved irrigation technologies. There is a great potential for further increasing agricultural water productivity by reducing water losses in irrigation systems, improving on-farm water-management practices, implementing demand management measures, improving operation and maintenance of the infrastructure, and shifting to less water-intensive crops.
Many countries are working to increase water productivity in agriculture. Water sector reform following the political change in South Africa, for example, has prioritized agricultural water demand management. In Indonesia, the main thrust of the water-reform process has been to increase agricultural productivity and improve the performance of irrigation, based on participatory management, developing and strengthening water-user associations, and facilitating access to agricultural support services and microcredit. In many areas, particularly in Asia and North Africa, rehabilitating irrigation waterways, reclaiming waterlogged and salinized lands, and recapturing lost storage capacity of reservoirs by dredging remain the biggest challenges.
A growing number of countries have been transferring the management of local irrigation subsystems to the farmers who use them, with the government usually retaining ownership of the infrastructure and management of the main system. In most cases, such management transfer reduces the costs of operation and maintenance, improves collection of water charges, increases water use efficiency, makes water distribution more equitable among users, and improves responsiveness. In Mexico, for example, recovery of operating and maintenance costs increased from 30 per cent to 80 per cent after the government transferred management of irrigation systems to user associations. In Egypt, cropping intensity nearly doubled in farmer-managed irrigation systems, and water-user associations were able to reduce some environmental impacts, such as the salinity level in runoff.
Those transfers of responsibility often occur in conjunction with reduction or elimination of government subsidies, resulting in increased water charges to farmers. That may pose financial difficulties for them, but also promotes more efficient use of the water.
Countries in South Asia have implemented extensive irrigation-improvement programmes ranging from lining of main canals to cooperative management of shared watercourses. High capital requirements constrain progress, however.
Adoption of modern water-saving technologies has been slowed by limited borrowing and repayment capacities of farmers, while credit programmes to promote these technologies have been hampered by inadequate governance mechanisms.
In many countries, demand management measures have proven successful in conserving water resources. Both developed and developing countries have reduced subsidies for irrigation water and increased cost recovery to improve the financing of water supply and improve efficiency.
Despite efforts to improve water efficiency in irrigation, scarce water is still often used for water-intensive, low-value production at the expense of uses that would contribute more to economic and social development. Changing water allocations, however, has proven difficult in many countries. In considering proposed irrigation projects, Governments often do not give adequate consideration to economic, environmental and social sustainability in the context of integrated water-resources management.
In many areas, particularly in Asia, poor management of irrigation has resulted in land degradation, reducing productivity or even rendering land entirely unsuitable for agriculture. Globally, about 20-30 million hectares of irrigated lands are severely salinized and an additional 60-80 million hectares degraded to some extent by waterlogging and salinity.23 An example of effective physical and demand management measures in addressing land and water degradation is the Murray- Darling basin in Australia. In another case, countries of the Nile Basin, with coordinated support by donors, are developing the "Shared Vision Programme" to create a coordination mechanism and an enabling environment for the implementation of water-management projects. On the other hand, delays in the implementation of planned initiatives in the Niger River Basin in West Africa are causing further damage to ecosystems and threatening the sustainability of many poor rural economies.
Many small island developing States and coastal zones are faced with the problem of salt-water intrusion as freshwater is pumped out of aquifers in the coastal zone, where most of the population lives. In such areas, simple "scavenger well" technology for extracting water from thin freshwater layers on top of deeper saltwater25 has shown positive results, for example in the Marshall Islands, but adoption of the technology has been slow owing to financial constraints.
In the case of water for hydropower, much of the potential in developing countries remains untapped. For example, sub-Saharan Africa and Central Asia are tapping only 17 per cent and the Asia-Pacific region only about 29 per cent of the economic hydropower potential and a much smaller share of technical potential.
That is in part because the locations of new resources and the demand for power are often poorly matched, with the further constraint of large capital requirements and environmental and social impacts. Dam sites on international watercourses may add further international complications.
Most developing countries are promoting development of their industrial sectors, often with serious implications for water pollution. Environmental regulations, including effluent standards, have not kept pace with industrial growth. In many developing countries, weak water governance and regulatory enforcement mechanisms have limited industry's incentive to invest in cleaner production technologies and wastewater treatment. While developing countries are not different in that respect from the currently developed countries during their own industrialization, they can benefit from the technological advances that have occurred in the interim which have improved the efficiency of input use, including water, and reduced material wastage, hence discharges to water and other media.
The sustainable management of international river basins is crucial for sustainable development. There are 59 international river basins in Africa alone, accounting for 80 per cent of the continent's surface water resources. International law has not progressed much in improving cooperation among riparian States. Many long-standing water-related disputes still remain unresolved, and the growing demand for finite freshwater resources heightens the risk of future conflicts. In OECD countries, the integration of upstream and downstream interests along transboundary water bodies is receiving increasing attention. In developing countries, the Mekong River Commission represents a long-standing mechanism for cooperation and coordination among riparian States, but the absence of key upstream riparians limits its effectiveness. Countries of the Nile Basin over the last decade have also been able to develop a common vision for efficient resource management and use.
