The withdrawal of freshwater from surface (rivers, lakes) or underground (aquifers) sources, at a rate faster than it is naturally replenished, is unsustainable and can ultimately deplete the resource. The Aral Sea in Central Asia is a dramatic example of the devastating environmental and socio-economic impact of unsustainable water withdrawal (UNEP 2002a and 2002b – Figure 2), while withdrawals of groundwater from the Ogallala Aquifer in the United States points to potentially harmful effects on the country’s agriculture and environment as the aquifer’s waters are depleted (Morris and others 2003).

Figure 2: Aral Sea degradation
The Aral Sea was once the world’s fourthlargest inland sea. Problems began in the 1960s and 1970s with the damming of the main rivers that feed it in order to grow cotton on arid land in what was then Soviet Central Asia. The surface of the Aral Sea once measured 66 100 km2. The sea is now a quarter of the size it was 50 years ago and has split into two.
	Source: USGS EROS Data Center/ UNEP-GRID - Sioux Falls	Source: USGS EROS Data Center/ UNEP-GRID - Sioux Falls
Source: UNEP-GRID Sioux Falls - Source: UNEP 2004	Source: UNEP-GRID Sioux Falls	Source: MODIS Land Rapid Response - Team at NASA GSFC

Figure 3: Estimated water use by sector, globally and regionally, for the year 2000

On the global scale, the agricultural sector accounts for over two-thirds of freshwater withdrawal (Figure 3). Industrial usecurrently accounts for a fifth of total global water use, while domestic use of freshwater was 10 per cent of global water use in the year 2000 (FAO 2003b). The proportion of water used for different purposes, however, varies between regions. The developing regions use relatively far more water for agricultural purposes, whereas the industrial sector accounts for the largest share of water use in the developed regions.

In the past 100 years, the world population tripled, but water use for human purposes multiplied sixfold (WWC 2000). There is much competition for water resources and in their allocation, the needs of ecosystems are often forgotten or ignored. This is due partly to our limited understanding of the complex linkages and dependencies between and within ecosystems, and of their relation to human needs and activities now and in the future. Ecosystems, which are subject to water stress become less robust and more prone to succumb to additional pressures. Aquatic ecosystems and their flora and fauna are especially at risk.