Naoise Ó Muirí (Dublin Bay North, Fine Gael)
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159. To ask the Minister for Housing, Planning, and Local Government the current allowable chlorine residual threshold in treated drinking water in Ireland; and if there a statutory upper limit under S.I. No. 99/2023. [64209/25]

James Browne (Wexford, Fianna Fail)
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S.I. No. 99/2023 does not specify a statutory upper limit for chlorine in drinking water. However, these regulations do set parametric values for chlorate and chlorite* which are compounds containing chlorine, reflecting the recast Drinking Water Directive requirements.

Water suppliers add chlorine during drinking water treatment to disinfect the water to kill harmful bacteria, thus ensuring the water is safe to drink.

The World Health Organisation recommends an upper guideline value of 5 mg/litre for free chlorine**.

The Environmental Protection Agency advises that at least 0.1 mg/l of free chlorine should be maintained within the water supply network to ensure adequate disinfection throughout the entire distribution system.

* chlorate and chlorite parametric values are applicable from 11 January 2026.

** free chlorine is the amount of chlorine available in water that is available to disinfect the water.