The United Nations Environment Programme and the World Health Organization wish to thank all those who have taken part in the preparation of this publication, in particular the two principal authors: Dr S. Cairncross of the London School of Hygiene and Tropical Medicine, and Dr E. A. R. Ouano, consulting engineer, Manila, Philippines. The authors drew heavily on a training module prepared by the United Nations Centre for Human Settlements (Habitat), whose cooperation in providing this material is gratefully acknowledged. Finally, thanks are due to GTZ (Agency for Technical Cooperation, Federal Republic of Germany) for its generous financial assistance, which made possible the publication of this book.