About three-fifths of the world's population lacked access to basic sanitation; and one-third did not have access to safe drinking water. Four in five of these unserved people are in Asia, with approximately one in five in both India and China, respectively. In rapidly developing countries, such as Mexico, the People's Republic of China, and the Philippines, new public health problems often emerge before the old ones have been solved, and it is important to assess which problems pose the greatest risks to health, and which solutions are most cost-effective.

Holistic environmental sanitation has four main water-related aspects: water supply, rainwater drainage, Solid waste disposal, and Excreta disposal.