direct electric current between said surface as an anode and said contaminated water at a density of 1.5 to 3.0 mA per square centimeter of said surface,(1) the area F of said surface in square centimeters and the flow rate V of said stream in cm3 /second satisfying the relationship F ??? c ??? V, wherein c is a factor whose numerical value, in sec/cm, is at least equal to the numerical value of