Few projects in the rural water supply and sanitation (WS&S) sector have achieved full sustainability, according to this study. The study, written to assist in the planning and management of WS&S projects, can also be used by evaluators as a checklist of level of sustainability; it focuses more on water supply than sanitation issues. The study reviews some of the literature and defines sustainability (Chapter 2); considers factors affecting sustainability (Chapter 3); discusses how sustainability is measured (Chapter 4); and ends with conclusions and recommendations. Appendixes contain case studies from Lesotho and Indonesia, which represent two distinct approaches to WS&S development. The Lesotho case is an example of a large USAID-funded project which had considerable success in providing water supply services to a large segment of the country's rural population. Much emphasis was placed on improving the institutional capacity of the government agency responsible for rural water supplies. The Indonesia case, in contrast, was an endeavor managed by an NGO, CARE, using USAID and other funds. Most of the communities involved had little subsequent contract with CARE or government water agencies after their particular project was completed, nor did CARE attempt to build government agency capacity or contribute to policy dialogue; rather, it emphasized the role of the communities, as institutions, in managing their own facilities. Project benefits in both countries were found to be sustained on a class II I level (third best a scale of four), in which benefits drop down to a stable level somewhat below the end of project status. The report identifies the following guidelines for planning sustainability; identify and assess the beneficiaries; involve beneficiaries and other stakeholders in project design; review community management resources; select appropriate technologies; develop a reliable operations and maintenance system; ensure financial viability of ongoing operations; recognize the development limits of the natural resource base; and be flexible and ready to change approaches.