We developed an up-to-date European map of groundwater pH and Ca (the major determinants of diversity of wetlands) based on 7577 measurements. In comparison to the existing maps, we included much a larger data set from the regions rich in endangered wetland habitats, filled the apparent gaps in eastern and southeastern Europe, and applied geospatial modelling. The latitudinal and altitudinal gradients were rediscovered with much refined regional patterns, as is associated with bedrock variation.