On a global scale, the problem of water is more a case of distribution and quality than one of quantity. Water is rarely a region-wide concern, with some notable exceptions, but all regions have some problems related to either ground-water or surface water resources.

The development and efficient management of water resources is of particular concern in West Asia and parts of Africa, particularly the Sudano-Sahelian belt and the Horn of Africa. Not only is there relative scarcity of water resources, but these locations also face high evaporation rates, high levels of anticipated future demands, and the transboundary problems associated with water resources. Measured against the future requirements of urban centres, agriculture, and industry, access to adequate quantity and quality of water will soon become problematic in those areas of West Asia, Africa, and the parts of Latin America that have mega-cities. In some cases, competition for water may lead to conflicts over transboundary resources.

In other regions, overexploitation of surface waters disrupts flow regimes, affecting aquatic ecosystems and the quantity and quality of water supplies downstream, a situation that can lead to hostility between water users. Overexploitation of ground water lowers water tables, which may damage wetlands, cause ground subsidence, and induce salt-water intrusion in coastal aquifers.

Many cities world-wide that depend on ground water as the primary water supply are experiencing problems caused by the deterioration of these reserves. In large cities in many regions, the discharge of inadequately treated sewage subjects aquatic communities to severe deoxygenation and possibly ammonia toxicity. Humans risk microbial infection if recycled water is not adequately treated, as happens in areas marginal to cities, including those mega-cities in the less developed parts of Asia and Latin America.

Europe also suffers from contamination of much-needed ground-water resources as well as shared surface water resources as a result of excessive agricultural fertilizer and pesticide use. Concerns over water in North America relate mainly to municipal supplies and rural water quality and their consequent impact on health.