Water sanitisation device, system and method

A method of sanitizing a body of water in a swimming pool or spa, including the steps of:

• adding sodium chlorite and/or sodium chlorate to the body of water;
• adding hydrogen peroxide to the body of water;
• converting the sodium chlorite and/or sodium chlorate to chlorine dioxide in an electrolysis cell which is in fluid communication with a water circulation system of the body of water;
• detecting a level of chlorine dioxide present in the body of water with a sensor;
• and
• stopping or slowing the electrolysis cell when the sensor determines that the level of chlorine dioxide present in the body of water has exceeded a predetermined threshold, wherein 0.05 to 0.5 grams of hydrogen peroxide is added per thousand litres of the body of water.

A water sanitization system comprising:

• an electrolysis cell arranged in a water circulation system of a body of water in a swimming pool or spa, the body of water containing a) sodium chlorite and/or sodium chlorate and b) hydrogen peroxide, the electrolysis cell operable to convert sodium chlorite and/or sodium chlorate to chlorine dioxide;
• a control unit in communication with the electrolysis cell;
• and
• a sensor configured to detect a level of chlorine dioxide present in the body of water,
• wherein the control unit is configured to stop or slow the electrolysis cell when the sensor determines that a level of chlorine dioxide present in the body of water has exceeded a predetermined threshold;
• wherein the electrolysis cell is controlled by the control unit in the following way:
• high chlorine dioxide production if sensed chlorine dioxide level is less than 0.1 ppm;
• low chlorine dioxide production if sensed chlorine dioxide level is between 0.1 and 0.8 ppm;
• and
• no chlorine dioxide production if sensed chlorine dioxide level is above 0.8 ppm.