The question was raised about L. pneumophila building up immunity to low concentrations of ClO₂ around 0.8 ppm in hot water.
I am not aware of any literature demonstrating resistance to 0.8 ppm chlorine dioxide – either Legionella or other bacteria. You state that the level of chlorine dioxide in the hot water is around 0.8 ppm. Is that correct? We have never seen that level in hot water.