Article 20a of the German constitution

Article 20a of the German constitution contains the protection of the natural basis of life and this includes water.

By the way, the more detailed laws on water are all combined in the “Wasserhaushaltsgesetz – WHG”, the “law on water supply”. This law also contains guidelines, bylaws and more about ground and surface water.

Source: https://www.bmuv.de/themen/wasser-ressourcen-abfall/binnengewaesser/gewaesserschutzrecht/deutschland/das-wasserhaushaltsgesetz