The DVGW is the German Association of Gas and Water Experts, which lays down, among other things, the guidelines for the construction, testing and use of plants for the treatment of drinking water. The ÖVGW is the Austrian counterpart. While WRAS does a similar job in the UK. Devices bearing these test marks comply to local standards and may be installed in drinking water installations without further measures. Only tested devices are subject to strict testing with regard to the materials used, and hygiene.
A GS mark, CE mark or similar alone are no proof of compliance with the applicable requirements with regard to hygiene and process success in drinking water.