European Norm EN 1717 regulates the standards for the protection of drinking water from non-potable water. It also specifies the areas of application for safety valves by defining various categories of liquids. DIN 1988-100 supplements EN 1717 with some national regulations on the subject.
The regulations can be summarised as follows: A drinking water installation must never be connected to systems containing water not intended for human consumption without a suitable safety device.