Safely managed water, sanitation and hygiene (WASH) services are viewed as fundamental for human wellbeing, enabling a range of positive outcomes related to health, education, livelihoods, dignity, safety, and gender equality.

However, progress in providing WASH services and thus achieving these outcomes has not occurred equally, with a range of inequalities in who can access and benefit from WASH services across varying socio-cultural contexts, geographical areas and socioeconomic settings. As the COVID-19 pandemic disproportionately affects particular groups of people, it has the potential to exacerbate many of these existing WASH inequalities.

Gender inequalities related to WASH are particularly large, as women and girls have specific needs related to biological factors, and experience strongly gendered norms surrounding water and sanitation. These inequalities extend beyond the household, with women and girls, and socially marginalised groups often under-represented in decision-making processes at all levels of WASH governance. WASH-related inequalities are also experienced by sexual and gender minorities, and can be shaped by other factors, such as caste relations and homelessness.

Awareness of these inequalities has resulted in implementation of WASH interventions that include the mainstreaming of gender and social equality (GSE) considerations. However, despite the wide range of GSE outcomes associated with WASH interventions, evidence has often been anecdotal, based on assumptions, or reported only in the grey literature. This may be related to the challenges of measuring social change, often a complex, nonlinear, context-specific, and slow process.

This review aims to comprehensively and transparently synthesise evidence on gender and social equality outcomes in complex WASH interventions. The authors also aim to develop and test a set of hypotheses about causal relationships between WASH intervention components and outcomes, related to their theory of change for promoting gender and social equality through WASH interventions. Their aim is to advance evaluation practices in the WASH sector by providing methodological advice on how to include, assess and measure GSE outcomes. Additionally, they will map definitions of different outcome measures and provide guidelines on this.