The present invention relates in general to the field of electrochemical water treatment systems and in particular to electrochemical water treatment systems containing a power controller for an electrically driven water treatment device. The power control unit comprises a main power supply unit, a slave power supply unit having a control input, a PLC having inputs from a current sensor and a voltage sensor and outputs for said main and slave power supply units. Said current sensor is adapted to measure the electrical current flowing through the cells of the purifier, said voltage sensor is adapted to measure the voltage applied to the cells of the purifier, and said PLC is programmed to be able to maximize the electrical power supplied to the cells without overheating.