A water pressure regulator (9) for a watering system (1) of an animal house (H) is provided with a water inlet member (51) comprising a watering path (73, 121) and a flush path (75, 123). The watering path is operably engaged by a regulating valve. The inlet member (51) is manually movable relative to the housing (21), to position the watering path outlet relative to the regulating valve to prevent the regulating valve from engaging the inlet member, thereby placing the regulator in a flush mode. The flush path (75, 123) has a water exit into the regulator spaced from the watering path port, and hence is not engagable by the regulating valve. A flush valve (85) is provided in the flush path, and is moveable between a closed position in which the regulator will operate in a drinking mode and an open position in which the regulator will be in a flush mode. An actuator (89) is provided which is operated by a control system to allow for automatic flushing of the watering line according toa predetermined schedule. Hence, the regulator can be switched between an operating mode and a flushing mode either manually or automatically. The control system can also control the lighting system and water supplement system for the animal house; and the control of the watering system can be tied to the lighting and medicating systems.