Water systems, medical equipment, and apparatus for thermal disinfection comprise a control unit which starts the disinfection of a fluid path by controlling a heating unit to heat water and controlling an actuator to enable heated water to flow into the fluid path. The control unit reads the temperature as measured by a temperature sensor during the disinfection and calculates an achieved disinfection dose. The achieved disinfection dose is compared with a set disinfection dose and the disinfection is discontinued if the achieved disinfection dose corresponds to the set disinfection dose.