The greatest impact of the Potable Water Project in Thailand was not health-related, but occurred in the form of economic benefits such as increased gardening, livestock raising, and crafts production. This surprising conclusion is a primary finding of this project evaluation. Some 250 water systems were constructed under this project, with an additional 550 systems built later by the Thai government. An estimated 17% of the rural population is now served by piped potable water as compared to only 3% prior to the project. Most of these water systems are not only still operating, but also financially self-sufficient, with users paying full costs of maintenance and operation. With only a few exceptions, operators appear competent and motivated, and have received consistent supervision from the Rural Water Supply Section of the Thai Ministry of Public Health. The economic, social, environmental, and health impacts of the project are evaluated. Although lack of initial baseline and village-specific health data prohibit confirmation of claims that health has improved, the convenience of direct, reliable water delivery close to villagers' homes has resulted in considerable time savings and increased water use, both of which have contributed to the above mentioned economic benefits. At first, almost all socioeconomic groups benefited equally from public-tap access. But as revenues lagged, metered private connections had to be installed to finance systems' operations -- effectively cutting off the poorer villagers from service. The success of the water systems were found to have resulted from initial community contribution of time, labor, and funds; training and subsequent support for local operators; and the evolution of viable rate structures for delivery of water to rural households. It is recommended that piped water projects be considered and planned not just for health gains, but for their economic benefits as well. Other recommendations, some generally applicable to A.I.D. projects, others specific to water projects, are included.