Water Supply and Sanitation Decade, a panel of experts prepared a two-volume report (text and appendices) on water quality -- defined in terms of wholesomeness and palatability -- and its role in devising rural water supply (RWS) programs in developing countries. Discussed in turn are the historical development of water quality standards; contemporary techniques for assessing water quality and the difficulty of applying these standards in developing countries; and trade-offs between the quality and availability of water in RWS programs. Contemporary water quality assessment relies heavily on the same techniques, albeit more sophisticated and complex, employed since the turn of the century. The principal techniques are sanitary surveys -- field investigations examining environmental surroundings and potential routes of water source contamination -- and multivariate chemical and biological analyses to detect bacteria and toxic contaminants. In the United States and Europe, regulatory standards (based on laboratory analysis guidelines) have been adopted to ensure water quality. Considerable controversy exists, however, on the uniform application of these highly sophisticated, urban-based standards and techniques to developing country RWS programs. Strict application of developed world standards may unnecessarily condemn developing country RWS's and lead to the use of more peripheral and lesser quality sources. Development experience shows that, in addition to chemical and biological requirements, water quality standards should depend on the availability and costs of water treatment technology, the plausible alternative investments in public health (waste removal, health education), the number of persons exposed to the water source, and local practices concerning palatability and water use. In designing RWS systems, the managerial and operational requirements contingent to water quality (i.e., continuous treatment of the water) must be guaranteed because the simple provision of water can be counterproductive if its quality is harmful.