Drinking water report shows persistent toxin in public supplies

The number of people served by “at risk” public water supplies increased again in 2023 to 561,000, up from 481,000 in 2022, according to the Environmental Protection Agency’s (EPA) annual report on drinking water.

Deterioration in supplies was mainly due to detections of persistent levels of toxic trihalomethanes (THMs) and the parasite cryptosporidium, which can make people ill — especially those with weak immune systems.

One in 20 supplies failed to meet the THM standard in 2023, affecting 300,000 people, up from 235,000 in 2022 — an issue repeatedly highlighted by the EU as the chemical, which can arise as a byproduct of disinfection, has been linked in some studies to cancer.

“Greater effort is needed by Uisce Éireann to implement improvements at supplies to minimise exposure to THMs, including at big supplies such as Limerick city, and Kilkenny city,” it warns.

THMs can form when organic matter present in drinking water reacts with chlorine. Some studies have suggested a link between cancer and long-term exposure (over years) to THMs and also that THMs can affect reproduction. There is some evidence that THMs cause cancer in animals, and as a result, they are classified as “possibly carcinogenic” to humans.

The European Commission started infringement proceedings against Ireland in 2015 for failure to comply with the drinking water directive THM standard. The EU Court of Justice ruled in January that Ireland had failed to fully implement the directive concerning THMs in 30 supplies.

While “the quality of drinking water from public supplies remains very high, with over 99.7 per cent of samples compliant with bacterial and chemical limits”, the resilience of supplies must improve and will require sustained investment into the future, according to the EPA.

The number of long-term boil water notices was 46 in 2023, almost double the number in 2022, it adds, while “progress to remove lead from our supply networks to protect public health is far too slow”.

Too many supplies still lack robust treatment measures to guarantee their long-term resilience and safety, the report warns.

The EPA’s remedial action list (RAL) identifies “at-risk” supplies that require improvements by Uisce Éireann to safeguard public health. While 10 supplies were removed from the RAL following improvement works, the EPA identified a further nine “at-risk” supplies.

Good progress has been made in other areas such as disinfection, progressing of the drinking water safety plan approach and making the lead remediation grant easier for the public to access, it finds.