Chlorine dioxide
Chlorine dioxide is not a restricted heavy metal like copper. It has proven excellent control of "Legionella" in cold and hot water systems and its ability as a biocide is not affected by pH, or any water corrosion inhibitors such as silica or phosphate. However, it is 'quenched' by metal oxides, especially manganese and iron. Metal oxide concentrations above 0.5 mg/l may inhibit its activity. Monochloramine is an alternative. Like chlorine and chlorine dioxide, monochloramine is approved by the Environmental Protection Agency as a primary potable water disinfectant. Environmental Protection Agency registration requires a biocide label which lists toxicity and other data required for all registered biocides. If the product is being sold as a biocide, then the manufacturer is legally required to supply a biocide label, and the purchaser is legally required to apply the biocide per the biocide label. When first applied to a system, chlorine dioxide can be added at disinfection levels of 2 ppm for 6 hours to clean up a system. This will not remove all biofilm, but will effectively remediate the system of "Legionella".