Monitoring of water, sanitation, and hygiene (WaSH) is necessary to track progress, improve accountability, and demonstrate impacts of efforts to improve WaSH conditions and services. Particularly in low-resource settings, there is currently no standard method for selecting WaSH indicators, which are necessary for robust monitoring and evaluation. To address this need, we first conducted a systematic literature review of existing indicator selection methods used in environmental science, international development, and other related fields. Based on findings from the systematic review, we then developed a WaSH indicator selection method, which includes the following stages: (1) defining concepts and purpose; (2) selecting and justifying a conceptual framework; (3) developing a list of candidate indicators; (4) determining selection criteria; (5) scoring indicators against criteria; and (6) selecting the final suite of indicators. Finally, this method was applied to the selection of indicators for school WaSH, and these final twenty indicators were organized into an input-output-outcome- impact framework. The resulting suite of school WaSH indicators provides a foundation for coordinated monitoring, identifies focus areas for resource allocation, and highlights needs for policy development in WaSH.