Over 100,000 are at risk of contracting cryptosporidium infecting by drinking water from factories that are failing to eliminate the parasite.
Dr Tom Ryan, Head of enforcement at the Environmental Protection Agency said that the increase of the parasite in water supplies is a worry because of the effect it can have on human health.
Of these plants seven had no process in place to deal with i, eight plants had inadequate processes to deal with it while three were able to deal with it but failed to do so.
Currently there are 16 plants that supply water to over 110,000 people that fall into these categories.
These include small plants in Laois.
Ireland has 804 public water plants serving over 1.3 million households.
99 percent of there plants passed the key qualities test last year but breached the pesticide and chemical limit which has caused other problems to worsen.
Irish water said that new monitoring procedures were devised in 2018 so these issues can be caught quicker and dealt with.