Water for the world —why is it so difficult?

Lack of clean water is the single biggest cause of human illness and death in the world. One of the UN's Millennium Development Goals is to halve the proportion of people lacking access to clean water and sanitation by 2015. But, while the technology underpinning water and sanitation in developed countries has been understood for nearly a century, it is proving difficult to transfer it to developing and transitional countries. This paper examines the evolution of water supply and sanitation in developed countries and identifies the challenges they are facing, including ever-increasing demands for higher quality standards, the need to replace ageing assets and demands for sustainability. It then questions how much of this is relevant to developing countries, where ‘sustainability of water supply’ simply means what is available today will continue to be available tomorrow.