The International Decade on Drinking Water and Sanitation, 1980- 1990, designed to bring clear water and sanitation to 1.5 billion people in developing countries, will fail unless community participation, with special emphasis on women, is incorporated into all rural water supply projects. So concludes this A.I.D. study of the meaning of community participation, how it relates to project success, and why women must be central participants. The author maintains that projects should be classified as "service" or "development" projects according to user perceptions. "Service" projects require no social change of the community in order to receive project outcome, have the assent of the local people, and can be implemented with the help of local leadership. A "development" project, however, is perceived by the community to require reorganization of social beliefs and organizations. To be effective, such projects require community participation, defined by Paulo Freire as a learning process of reflection/action/reflection through dialogue. Since women are traditionally responsible for water management and family education in most developing countries, their contribution to this learning process and dialogue is essential. The author develops a four-point operational framework for such local learning systems (LLS): (1) comparison of proposed technology to the technology currently used in terms of type and amount of change; (2) defining the learning process as one of community participation; (3) gathering pertinent information; and (4) decision-making. Current "development" projects fail when they attempt to use minimal community participation strategies suitable only for "service" projects rather than follow the entire participatory learning process and the LLS operational framework needed for their successful implementation. It is noted that the continued use and maintenance of a water system 5 years after project support has ended is a sure sign of genuine community participation -- and hence of project success. A 99-item bibliography (1966-79) and an overview of A.I.D. activity in water supply projects are included.