Improving water pollution control capacities in large cities

The urbanization process fundamentally affects the supply and quality of freshwater resources. With the building of roads, parking lots, shopping centres, houses and other buildings there is a loss of permeable soil surface through which rainwater can percolate down into the soil and into groundwater aquifers. Vast impermeable urban surface areas also have the effect of increasing the rate of evaporation of surface water and the movement of a greater mass and variety of pollutants in stormwater runoff. Thus, polluting materials applied to the urban land surface can be rapidly transported to surrounding areas, including drinking water supplies, rivers and seas.

This strategy features in the framework of Agenda 21 as formulated at UNCED (Rio de Janeiro, 1992), now coordinated by the United Nations Commission on Sustainable Development and implemented through national and local authorities.