Almost one quarter (23%) of Ireland's largest waste water treatment plants are not meeting EU standards, according to a report by the Environmental Protection Agency.
The report - Focus on Urban Waste Water Treatment in 2013 - also shows some water supply systems have no sewage treatment at all.
It said 38 of the largest waste water plants in the country are not reaching EU standards when it comes to treating sewage properly.
The report shows 44 areas had no waste water treatment and are discharging raw sewage, in some cases straight in to the sea.
The EPA says the situation needs to fixed and infrastructure needs to be improved.
Irish Water says the treatment of waste water in Ireland is inadequate and its task is to improve water infrastructure over a number of years.
Standards have increased since 2012 when the EPA found almost half of Irish waste water treatment plants failed to meet EU standards.
In addition to what it has been identified in the EPA report, the EU has taken proceedings against Ireland for failures to implement in full the 1991 Urban Waste Water Treatment Directive.