Germany's Federal Environment Agency estimates that a quarter of all German groundwater contains excessive concentrations of nitrates - threatening some communities' water supply. The cause is over-fertilization of farmers' fields. Germany, Austria and Switzerland have been successfully joint-monitoring Lake Constance water quality for years.
But authorities in Lower Saxony are only beginning to tackle the problem. Drinking water there often exceeds the EU norm of 50 milligrams of nitrates per liter.