The invention relates to a device for physically treating drinking water, in particular, for reducing the formation of limestone. The invention device comprises at least one water inlet (3b) and at least one water outlet (3c), whereby the device is mounted in the cold water supply line (3) of at least one water heater (1), preferably a boiler, and the device is placed in good heal-conductive thermal contact with the hot water area of the water heater (1).