Abstract: A method of killing bacteria or inhibiting growth of bacteria especially in a potable water supply or a hot water supply for personal washing purposes, comprising subjecting the water to an electrostatic effect of sufficient intensity to kill or inhibit the growth of bacteria, and a device for carrying out the method; said device being preferably located in the elbow of a water pipe so as to extend along an adjacent pipe length and comprises a cylindrical collar 1 mounted on the exterior of ducting means (13 or 12') and preferably at an elbow region (11 or 11') with said collar 1 having a passage therethrough and leading to a passage in the ducting means, an elongate tubular housing 3, preferably of polypropylene, closed at one end 4 and having at its other end, a flange 3' abuttable against the shoulder 2 or collar 1 via the intermediary of sealing means 5, and a close fitting electrode 7, preferably of solid copper or brass, insertable into said housing 7 via the opening of the collar 1 and having terminal