Abstract: A method for providing biological control to a flow of water in a recirculating potable hot water system. In such a system, water is subjected to an initial chemical treatment using an oxidizing biocide such as chlorine dioxide or peracetic acid that rapidly kills biofilm and Legionella bacteria. This treatment is continued until existing Legionella bacteria and biofilm are controlled. Once the bacteria and biofilm are controlled the chemical treatment is stopped. Starting concurrently with the chemical treatment or at the termination of the chemical treatment, non-chemical water treatment is provided. The non-chemical water treatment maintains the water system in a condition which is free of Legionella bacteria and biofilm. Chemical water treatment may be repeated intermittently should it prove desirable or necessary.

Abstract: Water in a recirculating hot potable water system 110 is treated by power pulses, by placing a coil 18 near the water and providing to the coil 18 an AC power source 12. The power source 12 is connected in a first loop with the coil 18 and a switch 20 during at least a portion of a first half-cycle of the AC power source period. The switch 20 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. Preferably, the water is treated chemically as well 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.