Raw sewage is flowing into the environment from 35 towns and villages every day, including Arklow.
The latest report from the Environmental Protection Agency has highlighted 113 locations where Irish Water needs to prioritise wastewater treatment to protect public health and the environment.
It also found that 19 large towns and cities, including Dublin and Cork, have failed to meet EU standards to prevent pollution.
Plans are moving forward to provide a waste water treatment plant for the town of Arklow.
However Senior Inspector with the EPA, Noel Byrne, says despite some improvements, Irish Water has repeatedly revised its plans to fix infrastructure issues.
The report also found that the Ringsend plant in Dublin repeatedly fails the treatment standards because it does not have the capacity to effectively treat all the sewage it receives
Irish Water says that it's upgrading the Ringsend treatment plant and advises it will be completed in 2025.
It says the amount of untreated and inadequately treated wastewater being discharged has fallen by half since 2014.