Almost 800 million people lack access to basic water supply, and almost 2000 million lack access to sanitation. Therefore, achieving universal access remains a crucial goal of the global development agenda. In order to shed light on whether international aid might help accomplish that goal, this study evaluates its impact in a sample of 121 developing countries during 1990–2015. A new approach is adopted in which aid affects access not only through provision of infrastructure (supply) but also through health education (demand). Additionally, the long-held concern about the persistence of impacts over time is addressed by estimating panel vector autoregressive models (PVAR). The results show that both supply- and demand-side interventions financed by aid can contribute to promoting access to water, but consistent long-term investments are needed.