Ensuring everyone has access to appropriate WASH facilities is one of the most fundamental challenges in international development. Researchers and funders need to consider carefully where there is the need for new primary evidence, such as impact evaluations, and for new evidence syntheses, such as systematic reviews. 3ie evidence gap maps are collections of evidence from impact evaluations and systematic reviews. They highlight where there are sufficient impact evaluations to support systematic reviews and where more studies are needed. Maps help decision-makers target their resources to fill these important evidence gaps and avoid duplication. They also facilitate evidence-informed decision-making by making existing research more accessible.

This evidence gap map eight-page brief suggests priorities for future research including:

• understudied outcomes such as sustainability and slippage, time use, musculoskeletal disorders, psychosocial health, safety and vulnerability;
• final outcomes such as education, income and poverty;
• alternative mechanisms such as community-led total sanitation or community-driven approaches;
• collecting data on objective measures of gendered behaviour change, health and socio-economic outcomes;
• sex and age disaggregation and explicitly employing gender analysis to better understand not only differential outcomes, but also the role of gendered norms and discriminatory social and structural barriers
• synthesising the evidence in areas with sufficient impact evaluations, such as WASH in schools and water use and treatment behavioural outcomes, using mixed methods approaches to provide evidence on effectiveness and implementation.