A new type of electrochemical reactor for use in electrochemical water disinfection was tested. To solve the problem of the formation of calcium carbonate scales on the cathode surface a cathode which simultaneously acts as a sonotrode was used. This sonotrode is an efficient means for in situ cleaning the cathode surface from calcareous deposits formed during hydrogen evolution from potable water. The production rate of active chlorine from potable water in the new reactor in dependence on current, ultrasound intensity, and flow-through velocity was measured. The production of active chlorine is not significantly changed by the effect of ultrasound.