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.
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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.