Tools are needed to inform decision-makers as they seek to improve water supply capacity from source protection to operational efficiency. This paper presents a methodological approach to build a decision-support tool that can account for natural system characteristics, water utility operations, and social dynamics. The method starts with an analysis of metrics to index performance and assess natural conditions. As an example metrics for surface water supplies in Maine illustrate the availability and reliability of measures that can serve as indicators. relative performance and capacity. Based on public and accessible information, a total of 33 metrics have been identified that provide information on the biophysical, operational, and social domains that affect the production of safe drinking water