Sewage from the equivalent of 77,000 people in 36 towns and villages is released into the environment every day without treatment.
Half of the raw sewage comes from Arklow, Cobh and Kilmore Quay, according to the Environmental Protection Agency.
There are also 21 large towns and cities, including Dublin and Cork, where waste water treatment did not meet EU standards.
Meanwhile, Irish Water says it's working to deliver an "unprecedented" level of investment in wastewater treatment.
The utility will spend 400 million euro next year.
Irish Water, says trouble acquiring land has held up some projects.