UP to 30 public water supplies have restrictions in place at any given time, some of which date back years.
One dates from 2007, at The Strand supply in Co Laois. The Environmental Protection Agency (EPA) has begun enforcement action against Laois County Council after failing to carry out works to make it safe.
"It serves three houses, and the treatment plant isn't up to scratch," an EPA spokesman said.
"The first enforcement notice issued in September 2012, and we became aware of it the previous July. The local authority said the supply had been on a boil notice for as long as anyone could remember. We put it at 2007 as this was when we became responsible.
"There was E-coli detected and they failed to notify us. We have an enforcement notice issued and it should have been complied with."
Restrictions are also in place in Bruff, Co Limerick, and Ennis, Co Clare, since 2008, because there is lead in the system.
Kenmare and Mountain Stage in Kerry have restrictions since 2009, while eight have been put in place this year – the most recent in Kiltimagh, Co Mayo.