a water treatment apparatus for treating water in a device using water as a circulating medium comprises an extractor line for removing water from the device and ozone generation means for producing and conveying a supply of ozone . a contactor / mixer member is provided and has an entry passage for receiving water from the extractor line and ozone from the ozone generation means . the contactor / mixer member has contacting passages for receiving a water and ozone mixture from the entry passage and is configured so as to create turbulence to intimately mix the water and ozone along at least a portion of its length . a return line is provided for receiving and transporting the water and ozone mixture from the contacting passages back to the device .