Monitoring of water services informs policy and planning for national governments and the international community. Currently, the international monitoring system measures the type of drinking water source that households use. There have been calls for improved monitoring systems over several decades, some advocating use of multiple indicators. We review the literature on water service indicators and frameworks with a view to informing debate on their relevance to national and international monitoring. We describe the evidence concerning the relevance of each identified indicator to public health, economic development and human rights. We analyze the benefits and challenges of using these indicators separately and combined in an index as tools for planning, monitoring, and evaluating water services. We find substantial evidence on the importance of each commonly recommended indicator--service type, safety, quantity, accessibility, reliability or continuity of service, equity, and affordability. Several frameworks have been proposed that give structure to the relationships among individual indicators and some combine multiple indicator scores into a single index but few have been rigorously tested. More research is needed to understand if employing a composite metric of indicators is advantageous and how each indicator might be scored and scaled.