The world is moving into a period of widespread water stress and competition,with enormous implications for food security, the health of the aquatic environment,and social and political stability. In the second half of the 20th Century water demand more than tripled,the major factor being irrigation for food production. Over the same period,the number of large dams worldwide climbed from 5,000 to 45,000 - bringing about a major alteration of river hydrology and ecosystem function. Rivers have been disconnected from portions of their channels, their floodplains, their deltas, and from the seas into which they empty. The resulting loss of aquatic habitat has put freshwater life in grave jeopardy. In the 21st Century it will be possible to satisfy the needs of 8-9 billion people while protecting the health of aquatic ecosystems,but only with a fundamental shift in the way society uses, manages and values freshwater. It will likely require a doubling of water productivity over the next 25 years - including more efficient irrigation practices and greater recycling of wastewater. To guide policy, nations need to systematically determine their freshwater ecosystem flow requirements in a way that perhaps only South Africa is attempting so far. Underpinning all these measures is the need for a guiding water ethic that states that enough water should be provided for all living things before some get more than enough.

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