The overall quality of Irish drinking water is consistently high but, worryingly, the latest evaluation by the Environmental Protection Agency (EPA) shows up persistent problems. These include cryptosporidium, high pesticide levels and chemical byproducts of chlorination in too many supplies.

Cryptospordium is a parasite arising from human and animal waste that causes serious illness in people with weakened immune systems. It was detected in 25 public water supplies in 2018, up from 17 in 2017 and 12 in 2016. This indicates an absence of basic water filtration and prompted the EPA to require Irish Water – which is responsible for all public supplies – to submit cryptosporidium test results and indicate to what extent barriers or filters were in place and when the threat would be rectified.

The report for 2018 confirms a 98 per cent compliance across testing for microbes and chemical contaminants but the EPA’s “remedial action list” is telling. Besides cryptosporidium, high levels of disinfection byproducts, notably trihalomethanes (THMs), as well as “persistent pesticide failures”, are prevalent. These affect a great many consumers – 42 supplies serving 309,884 people were on the list for persistent THM issues. THMs are toxic compounds arising from a reaction between organic materials when chlorine is added as a disinfectant. The European Commission is prosecuting Ireland for continuing to exceed limits for them in drinking water.

Irish Water has pointed to improvements in its response to contamination problems and to significant progress on disinfection and pesticide excesses. Co-operation with other agencies and better management of river catchments has ensured progress on the latter front while improved testing enables more timely alerts.

The utility is investing €5.5 billion over seven years to improve water infrastructure and to address legacy issues it inherited when it was formed in 2013. The latest EPA evaluation confirms much remains to be done, particularly by targeting investment at the worst locations.