With support from the World Bank, the Costa Rican Institute of Aqueducts and Sewers (AyA) undertook the development of a project to estimate the seismic risk of its infrastructure including 65 water storage tanks located in the cities of San José and in some outlying residential areas. Thanks to financial support from the World Bank Water Partnership Program (WPP) and the Government of Australia, AyA was also able receive technical assistance from the Mexican company Evaluación de Riesgos Naturales (ERN). The result of this project was a risk estimate using two indicators: Annualized Loss Expectancy (ALE), and Probable Maximum Loss (PML). The first of these indicators is evaluated for both the entire portfolio and individually for each component within the AyA infrastructure network, while the second indicator is an estimate of the entire portfolio.