The philosophy of water supply is largely based on the urban experience of temperate countries which have relatively ample funds and where availability of sources is rarely limiting. The preoccupation with quality that this engenders may be inappropriate to the rural tropics when settlements are scattered. Since improved health is usually the chief reason given for improving supplies, rational expenditure of the limited funds for improvements requires an analysis of the relation of diseases to water. When funds are inadequate for ample safe water, the most relevant improvement will vary in different places; this requires increased flexibility and diversity in the responses of governments. The technologies involved in rural water supply are reviewed. Once improvements have been made, maintenance is a major problem. The crucial rural problems are more concerned with the social than purely technological aspects of supply. Increasing weight is now given to 'self-help' approaches, yet these await rigorous assessment. The problems of evaluating technological advances in their social setting have not yet been fully solved.