Abstract: The heater has various provisions which severally and in combination improve its life, protect it from overheating and burnout under all operating conditions, and adapt it for shower use with maximum safety. These include a special arrangement with a water pressure responsive switch of a heating unit of the type having a rigid tubular housing so as to effect adequate heating with relatively low current density, provision for confining the heating of said unit to portions thereof which are fully submerged in water during operation, provisions affording air chamber means for accommodating exudations from the heating unit and facilitating operation of the pressure responsive switch, provisions for lockingly enclosing its insulating electrical housing and for encapsulating with the aid of potting compound all electrical elements of the device.