Abstract: An electrolysis water purification system employs a fixed magnitude ionization current source the output of which is effectively pulse-width modulated, by controlled switching of the connection of the current source to the ionizing electrodes. As a consequence, ion production can be controlled as a percentage of water flow time (the period during which the filtration pump is operating) and is evenly distributed throughout the water to be purified. The output of a DC power supply is coupled through a controlled switching circuit to the ionizing electrodes. The controlled switching circuit includes a presettable timer-controlled switch that operates under the control of clock generator and establishes the duty cycle of the supply of ionizing current to the electrodes. The output of the presettable timer-controlled switch is coupled through a timer-controlled polarity reversing circuit to the ionizing electrodes.