Drinking water events in Derry area involved pesticide, iron, trihalomethane, discolouration, odour breaches

Seven significant drinking water quality events directly affecting tap water supplies in the Derry City and Strabane District Council area were recorded in 2022.

The events – classified as situations affecting, or with the potential to affect, drinking water quality – are listed in the Drinking Water Inspectorate’s (DWI) newly published annual Drinking Water Quality in Northern Ireland report.

Ten properties on the Baranailt Road in Claudy were affected by the ‘contamination of the mains water supply’ between February 3 and 5, 2022.

This, the report states, was caused by ‘ingress through an open hydrant during operational work to connect a new main’.

"Bottle water was provided to affected consumers and the main was chlorinated and flushed as a precaution," the annual report states.

Over May 10-18, 2022 a population of 41,681 straddling the Derry City and Strabane Council area and the Fermanagh and Omagh District Council area were affected by higher than permitted levels of a pesticide.

"Contraventions of the individual pesticide standard for MCPA [2-methyl-4-chlorophenoxyacetic acid, a phenoxy herbicide] occurred in the works final water due to insufficient treatment.

"A Regulation 31(4) Notice has been issued by DWI in respect of pesticide contraventions. NI Water have undertaken a major upgrade of this works in response to this Notice," the report states.

The same population of the Derg area was also affected by breaches of trihalomethane standards between August 16 and November 10 last year.

Trihalomethanes are 'a group of disinfection by-products that form when naturally occurring organic substances combine with chlorine, which is added to disinfect the water and make it safe to drink', the report explains.

"A contravention of the Total Trihalomethanes (THMs) parameter occurred in the works supply area due to sub-optimal treatment.

"NI Water have undertaken a major upgrade of this works," the report observes.

Meanwhile, a population of 119,178 people across the Causeway Coast and Glens Borough Council and the Derry City and Strabane District Council area was affected by issues at the Ballinrees Waster Water Treatment Works, which is located off the Windyhill Road between Coleraine and Limavady.

Between September 9, 2022, and October 5, 2022, 'contraventions of the taste and odour parameters occurred in the works final water and related distribution due to insufficient treatment', the report says.

"Consumer complaints regarding Taste & Odour in the Ballinrees WTW supply area were received by NI Water.

"A Regulation 31(4) Notice has been issued by DWI in relation to taste and odour contraventions at Ballinrees WTW,” the authors note.

Work underway on essential new water supply system from Campsie to Strabane

A larger number of people (180,817), split across the Derry City and Strabane and Causeway Coast and Glens districts were affected by 'elevated levels of turbidity and aluminium...in the works final water following loss of effective treatment caused by a dosing pump failure'. This breach, also at Ballinrees, occurred over November 5-6 last year.

The annual report also lists an issue with elevated levels of iron and discolouration affecting the tap water of 80 properties in the Ardmore area.

"Samples taken in response to consumer complaints contravened the iron and turbidity standards (including results above the Health Notification Values) due to the condition of the iron mains.

"Mains replacement is scheduled for 2023. NI Water put in place a mains flushing programme to reduce the risk for discoloured water as an interim measure until the mains replacement is completed," the report states, indicating that the issue was reported on November 8, 2022 and remained ongoing at the time of publication last week.

And last November (21-25) 79,501 people in Causeway Coast and Glens and Derry City and Strabane were affected by a breach of pH targets for acidity and alkalinity.

"A contravention of the hydrogen ion (pH) parameter occurred in the works final water. Following an investigation, NI Water was unable to identify the cause of the contravention," the report states.

According to NI Water hydrogen ion (pH) levels measure the degree of acidity of the water where a pH of 7 is neutral; values below 7 are acidic and above 7 are alkaline.

"A low pH water may result in pipe corrosion. This is corrected by adding alkali during water treatment."

Colin Clements, Interim Chief Inspector of Drinking Water, noted that the contraventions were the exception rather than the norm and that across the north drinking water compliance is generally good.

“Overall public drinking water quality for 2022 remained high with 99.91% compliance, a slight increase from 2021 (99.88%). Compliance at private water supplies was 99.02% a slight decrease from 2021 (99.19%),” he states.

Welcoming publication of the report, the Chief Executive of the Northern Ireland Environment Agency, Paul Donnelly said: “I welcome the Drinking Water Inspectorate’s annual report on Drinking Water Quality in Northern Ireland.

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"The report demonstrates that the quality of our drinking water remains high which is vital for the protection of Public Health. It is also important for the hospitality sector, farming and the economy.”

He added: “The Drinking Water Inspectorate has an important role to play in providing the Northern Ireland public with an independent assurance that their water supply is safe and clean.

"When required, DWI has carried out enforcement to ensure safe, clean drinking water is sustained.”

Mr. Donnelly said the continued improvement in drinking water quality remains a priority for the Department of Agriculture, Environment and Rural Affairs.

"DWI continues to use its influence with NI Water and the owners and users of private water supplies to improve drinking water quality regardless of where it comes from.

"The need to secure the provision of a resilient public water supply into the future as well as the need to achieve net zero is driving the need for more innovative, lower carbon treatment solutions to be identified by NI Water,” he said.

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