Water, sanitation, and hygiene (WASH) interventions prevent and control disease in humanitarian response. To inform future funding and policy priorities, WASH ‘gaps’ were gathered from 220 focus group discussions with people affected by crisis and WASH practitioners, 246 global survey respondents, and 614 documents. After extraction, 2,888 (48%) gaps from direct feedback and 3,151 (52%) from literature were categorized. People affected by crises primarily listed “services gaps”, including need for water, sanitation, solid waste disposal, and hygiene items. Global survey respondents primarily listed “mechanism gaps” to provide services, including collaboration, WASH staffing expertise, and community engagement. Literature highlighted gaps in health (but not other) WASH intervention impacts. Overall, people affected by crises wanted the what (services), responders wanted the how (to provide), and researchers wanted the why (health impacts). Our research suggests need for renewed focus on basic WASH services, collaboration across stakeholders, and research on WASH impacts beyond health.