Water in a recirculating hot potable water system 110 is treated by power pulses, by placing a coil near the water and providing to the coil an AC power source. The power source is connected in a first loop with the coil and a switch during at least a portion of a first half-cycle of the AC power source period. The switch is opened during a second half -cycle, during which a subroutine of producing at least a first ringing pulse in the coil assembly is performed. The water is treated chemically and by the power pulses. An improved water system has a water heater 112 and a circulation line 116 providing a flow loop. There is a tap 124 for diverting circulating water through an external loop and there is a pulsed power water treatment apparatus 122 mounted on the circulation line. A chemical treatment apparatus 126 is periodically connected to the tap.