Abstract: An ozone generator in which an air pump discharges air through a plurality of juxtaposed, successive, tubular housings, each of which has concentric wire mesh electrodes separated by dielectric tubes. A high a.c. potential, insufficient to cause a spark discharge, is imposed across the electrodes so that the oxygen of the air is progressively converted into ozone. The ozone laden air is directed through non-return valves into water flowing in a pipe for the purpose of destroying bacteria therein.