There is no central contact point. However, your water supplier is obliged to provide information about the different degrees of hardness in each supply area. Usually this information can be found on the website of your water or municipal utility. Please note that water hardness may vary from day to day, as your water supplier obtains and mixes water from different sources. In germany there are – depending on the region – water hardnesses between 0.358 mmol/l (2 °dH) * to approx. 7.16 mmol/l (40 °dH).
You can also learn interesting facts about your drinking water after a drinking water analysis in a laboratory. They will inform you about the most important parameters of your drinking water. This also includes the total hardness.
* 1 °dH = 0.179 mmol/l; 1 mmol/l = 5.6 °dH