Ozonators do sanitize water, but the process alone is insufficient to oxidize solids within the water. In most cases, the simple act of climbing into the water releases enough contaminants to overwhelm the ozonator’s efforts for hours. This leaves the pool unsanitized while in use. Maintain a chemical residual, however, and the spa stays clean even after guests drop in. Ozonators can reduce the need for chemicals in spas — and even in pools — but they cannot replace them.