Chlorine Dioxide Fluid Category

• Area of Interest: Water Quality
• Topic: Maintaining wholesomeness
• Title: Chemical dosing equipment for maintaining water quality
• Regulation/Byelaw Clause Reference: G26.1
• Reference Number:WQ03 00.53.03
• Decision Date: October 2000

Where equipment for continuous dosing of chemicals, such as chlorine dioxide, is proposed for use by owners or occupiers to maintain water supply quality in premises (e.g. to protect against the growth of Legionella bacteria), dosed water must be wholesome if used for drinking, cooking or food production purposes.

Where chlorine dioxide is to be used for this purpose, to ensure that dosed water is wholesome, the following conditions should be met by the operators of the equipment:

a) there should be evidence of the quality of the chlorine dioxide and its concentration e.g. use of chemicals with current DWI ‘Regulation 25’ approval;

b) there should be evidence of the effectiveness of the control of flow and chemical dosing device(s) i.e. evidence of the stability of the proportional control of chlorine dioxide against typical water flow rates that would be encountered in practice;

c) there should be evidence demonstrating that the 0.5 mg/l concentration of chlorine dioxide, chlorate and chlorite is not exceeded. This would require chemical analysis, for chlorine dioxide, chlorites and chlorates, of water samples from trial installations extending over several weeks.

d) there should be a programme for regular chemical analysis of chlorine dioxide, and, where significant background concentrations in the mains water supply justified it, by the measurement of chlorites and chlorates in the proposed installation.

Where these conditions are met, the chlorine dioxide dosing equipment is considered to be fluid category three and must have a suitable backflow protection for the connection feeding it. If these conditions are not met, it is recommended that the Water Supplier should inform the owner and occupier that drinking water taps supplied directly off the supply pipe should be installed in convenient locations and clear instructions should be given that taps supplied with dosed water should not be used for drinking, cooking or food production purposes.

In the event of reluctance by the owner or occupier of the premises to act accordingly, the Environmental Health Officer should be advised. These conditions could be used as a model for acceptability of other types of chemical dosing equipment used for similar purposes.