Two Inishowen water supplies fail to meet EPA standards

Two Inishowen water supplies have been identified as having failed to meet standards for levels of pesticides or trihalomethanes last year, a report from the Environmental Protection Agency (EPA) shows.

The Drinking Water Quality in Public Supplies report for 2021 shows that the Pollan Dam water supply was one of 58 public supplies that failed to meet the standard for trihalomethanes (THMs) in 2021 compared to 35 in 2020. The breach in standards, however, was not serious enough to have the water supply added to the EPA’s remedial action list (RAL), a record of the public water supplies known to be at risk and where the EPA is requiring Irish Water to take corrective action.

THMs form when natural organic matter such as rotting vegetation reacts with chlorine used in the disinfection treatment process. Long-term exposure to THMs may cause health risks. 

A supply may be placed on the RAL if there is a persistent failure to meet limits and processes are not sufficiently robust to reliably maintain THM levels below that level.  

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The Buncrana water supply was one of 31 that failed to meet the pesticide standard in 2021 but it was not one of the six supplies on the remedial action list for pesticides at the end of 2021. 

Pesticides are found in drinking water due to the incorrect use of such products in the catchment of water bodies used for drinking water supply. 

Pesticides include a wide range of products, but in Ireland, herbicides are most commonly found, in particular, MCPA18 which is used for rush control in grassland. Where pesticide failures are found, monthly monitoring must be carried out during the spraying season of April to November. A supply is considered to have a persistent pesticide problem if failures are found during four or more of the monthly sampling events. A supply may be placed on the RAL if failures are persistent and initial investigations fail to resolve the issue. 

The EPA says the quality of drinking water from public supplies remains high, with over 99.7% of samples compliant with bacterial and chemical limits.

It said, however, the increase in the number of supplies breaching THM standards reverses the progress seen in recent years. 

Progress to remove lead from drinking water networks is also too slow, the EPA observed,  with the need for stronger leadership at a national level. The report found the number of people served by “at-risk” supplies on the EPA’s RAL has reduced.