Although the world's growing population desperately needs more water it also needs more food, and these two opposing issues are colliding. However, just as gains in per-capita grain production now show signs of levelling off, new approaches to water supply and management will also ultimately reach their own limits. Over the longer term human populations will need to come into balance with available renewable water supplies.

The total amount of water available for human development, welfare and the ecosystem, is the same today as it has been throughout history. However the quality is poorer, distribution has changed and the rate of withdrawal has accelerated. Over this century the withdrawal has increased by a factor five whereas the population increase has been only a factor of three during the same period. The major reasons for this increased demand are industrial growth, increased urbanisation and change in life-style and the population growth.

Risks of increasing competition for the available water resources include;

• Deteriorating public health
• Food production insecurity
• Political conflicts
• Environmental degradation
• Restrictions on social and economic development.

To limit and cope with these risks we need to adopt new policies on a global scale. In the past, the relationship between population, environment and development was generally addressed separately. Conventional water management in the absence of social and environmental issues will obviously fail.

Climate Change

The transport of water and the energy exchanged as it is converted from one state to another are important drivers in our weather and climate. The behaviour of oceans and the wind are intimately related to global weather cycles, if land water run-off (to the oceans) is drastically reduced we be causing long term climate problems. Added to which there are serious questions over future water supply in light of global warming and the likelihood that we are inadvertently changing the climate world-wide through the heat-trapping greenhouse gases.

The impact of the predicted global warming on renewable water supplies and demand for water is unknown, but it is likely to change rainfall, storm patterns and sea levels.

Some preliminary studies have suggested as much as a 25 percent decrease in the runoff of the Nile and similar losses in the rivers of the south-western United States. Moreover, some climatologists predict global warming will intensify the extremes of the water cycle, i.e. increasing drought and bringing more floods.

In the USA the Midwest "dust bowl" has suffered searing drought in 1988 to record-breaking flooding five years later illustrating how damaging climate extremes can be. The risk of substantial changes in climate over the coming decades, coupled with the other threats posed by growing human pressures, underlines the uncertainty about future water supply.

At the Earth Summit in 1992, the governments of the world agreed that water resources must be managed sustainable, with full recognition of their limits.

AGENDA 21 is one of 5 documents agreed during the United Nations Conference on Environment and Development (UNCED). Signed by 179 Heads of Government, it is a blueprint for sustainable development in the 21st century, aimed at providing a high quality environment and healthy economy for all the peoples of the world. Chapter 18 of Agenda 21 deals solely with the protection of the quality and supply of freshwater resources.