Very low or very high concentrations of calcium (Ca) and magnesium (Mg) or total hardness in drinking water have been empirically recognized as the cause of the problems with corrosion, scaling, or taste of water. A large body of scientific evidence over the last 60 years has also attributed health problems to both extremes of these minerals in water. For example, drinking water low in Mg significantly increases the likelihood of cardiovascular mortality. This knowledge is not properly considered in the drinking water quality regulations, especially as more and more water is now produced by desalination disturbing its natural mineral composition. Although the current EU Drinking Water Directive does not include limits for hardness, Ca or Mg, most member states regulate these parameters either through law (12 countries) or technical guidance (7 countries), and several countries have issued educational information for the public. However, the regulations in most countries are not based on current research and not comparable because some provide a recommended range while others provide mandatory minimum or maximum limit values. This summary of the situation in 28 European Union countries is intended to provide information that can contribute to the implementation of the revised EU Directive.