A water flushing and sampling device (1) comprising a valve (33) operable to flush water from a subterranean source through the device. A turbine (73) downstream of an outlet nozzle (37) is operable to generate electricity when water is flushed through the device. An enclosure (13) contains the valve, a temperature sensor (81) operable to sense temperature within the enclosure, a heater (77, 83) operably connected to the turbine and being operable to heat the enclosure, and a control system (91) operable to open the valve to cause the turbine to operate the heater when the temperature sensor indicates the approach of a dangerously low temperature.