WaterAid and sustainabilityImprovements to water supply and sanitation services should deliver permanent benefits to their users. Similarly, hygiene and sanitation behaviour changes established now should last into the future. In many of the countries where WaterAid works, the systems and institutions needed to ensure sustainability are extremely weak or non-existent. Communities can struggle to keep services working on their own, and behaviour change improvements can be lost without continual promotion and reinforcement. Services can be threatened by poor management, insufficient financing, limited capacities, poor governance, climate variability, climate change, ecosystem degradation, pollution, and a growing demand for water resources. To achieve universal and lasting access to water, sanitation and hygiene by 2030, attention must be given to the sustainability of services and behaviour change.