Some 161,000 people are at risk of crippling illness from a microscopic parasite in drinking water, the Environmental Protection Agency has warned.
The agency said 25 supplies to homes, schools, hospitals and businesses around the country do not have adequate treatment to kill off the cryptosporidium bug.
Among them are 26,905 people living in and around Letterkenny, Co Donegal, where the improvements should have been finished in 2013.
There are another 62,066 people living under the threat of sickness from the parasite in the Killarney and Tralee areas of Co Kerry, and 19,689 people in Portlaoise, with upgrade works in both areas to be finished in December.
And 12,823 people are drinking inadequately-treated water in parts of Sligo served by the Lough Talt supply.
The EPA also warned that a herbicide increasingly used on marshy land is affecting up to 70 water supplies.
Pesticides
Darragh Page, senior drinking water inspector in the EPA's office of environmental enforcement, said on Tuesday Irish Water was being asked to provide – within one month – a national plan to outline how they will deal with the issue.
Mr Page said if pesticides are used on land before heavy rain they can be washed into rivers and lakes.
Mr Page said another common problem was if the container used to hold the pesticide was washed in a river. “A very, very small amount . . . Even in an empty container, the drops of pesticides in it are enough to contaminate a water supply.”
He said it was “absolutely crucial that Irish Water has an ongoing secure and sustainable source of funding” so it has the funding in place to complete these projects.
Mr Page said the biggest concern was the 25 supplies around the country that do not have adequate treatment for cryptosporidium.
“That means the water is taken straight from a river or lake and there’s no filtration on the supply, chlorine is added and that’s it. They serve around 161,000 people. That’s our highest priority.
“There’s a possibility that these supplies could end up on a boil water notice and they need to be fixed as soon as possible.”
Tap water standards
The EPA’s review of drinking water quality for 2016 said the number of supplies at risk from cryptosporidium reduced from 37 to 25.
As of this month, 87 supplies were still on the so-called Remedial Action List for work to be carried out to protect tap water standards.
The watchdog said that last year E. coli was detected at least once in three supplies, compared with seven supplies in 2015.
They were Newcastle Hospital in Co Wicklow, Aughclare-Campile in Co Wexford and An Ghraig in Co Kerry. All three issues were resolved within weeks, it said.
The EPA said more than 3,600 people still have to boil water every day in order to have a clean supply to drink.
The worst of those affects 3,427 people in Ballinlough and Loughglynn in Co Roscommon because of issues in treating cryptosporidium.