Water Coolers sit with non-chlorinated water in them on a daily basis. The makes regular sanitization necessary to keep cooler microorganism counts low. You can add chlorine periodically to a cooler then flush repatedly to sanitize or you can use ozone. There are two advantages to using ozone - Ozone is a much more powerful disinfectant than chlorine and it reverts to oxygen in a few hours leaving no chemical residual. Scientific studies have shown the rinsing fruits and vegetables in ozone treated water dramatically extends shelf life.