A control circuit is connected to sense the impedance changes in a transformer driven ozone generating circuit cause by inadvertent immersion in water of the ozone generating field and to respond by reducing the strength of the ozone generating field as result thereof. To retain some ozone generating usefulness during the presence of mist or vapors in the ozone generating field the control circuit includes a series connected operational amplifier in the feedback loop that while operating in its linear range effects a proportional feedback response to reduce the ozone output. In this manner the usefulness of ozone generation is extended during highly active periods in a pool or spa.