Over 400 million people worldwide use groundwater contaminated with arsenic and/or fluoride as a source of drinking water. The Swiss Federal Institute of Aquatic Science and Technology (Eawag) has developed a method to estimate the risk of contamination in a given area using geological, topographical and other environmental data without having to test samples from every single well. The research group’s knowledge is now being made available free of charge on the interactive Groundwater Assessment Platform (GAP, www.gapmaps.org). GAP is an online GIS platform for risk forecasting and mitigation of geogenic groundwater contamination. GAP enables researchers, authorities, NGOs and other professionals to visualize their own data and generate hazard risk maps for their areas of interest.