This evaluation looked at the performance and sustainability of 100 water systems that were installed in Paraguay between 2004 and 2010 as part of a project supported by the IDB. As part of the study, a technical review was conducted of the systems eight to ten years after entry into service, and interviews were held with users, sanitation boards, and the executing agency (SENASA). After establishing the level of performance, the evaluation studied factors that are correlated with a higher level of performance and sustainability, relative to both the original design parameters and the changing needs of the beneficiary communities. The evaluation found that the performance level of the systems is very high. Virtually all the systems built under the program are in service. Moreover, the users and the sanitation boards are satisfied with the quality of service in terms of water quality and reliability. Eight to ten years after installation, only 4% of the systems are not in service, compared with the rate of 20% to 25% that would be expected based on available data from around the world.