A water treatment apparatus is operated by providing water to be treated in a reactor; passing air through a gas flow path which includes an ozone generator wherein the passage of the air through the ozone generator produces ozone enriched air, and subsequently introducing the ozone enriched air into the reactor from the gas flow passage; providing an electric current source for powering the ozone generator; providing an member to emit a signal (preferably a visible signal) representative of the level of current drawn by the ozone generator; and, using a sensor to monitor the signal produced by the member.