Greywater is relatively clean wastewater – from showers, baths, bathroom and kitchen sinks, washing machines or dishwashers – which (unlike blackwater) has not been in direct contact with faeces. It accounts for almost 70% of all wastewater produced by Swiss households. After appropriate treatment, greywater can be safely reused for toilet flushing or irrigation. With advanced treatment processes, the quality and thus the potential for reuse of greywater can be further increased. Research on this is being conducted at Eawag in several projects. A new fact sheet highlights the associated opportunities and challenges.