This article assesses the impact of postconstruction support (PCS) on the sustainability of participatory, demand-driven rural water projects in the Cuzco region of Peru. This Study evaluates ninety-nine villages from two water supply schemes-projects built under a social investment fund program and those built under a nongovernmental program funded by the Swiss government. Overall, the study finds that the projects are performing very well. Multivariate regression analysis suggests that household- and village-level PCS is linked with financial performance, overall household satisfaction, and attitudes toward long-term future performance after controlling for project and community determinants of sustainability.