City and county councils have been seriously criticised by the Environmental Protection Agency (EPA) after it found that a majority of sewerage plants were not being run to minimum standards.
The agency has also said it will bring enforcement proceedings against the local authorities if there is not a significant improvement in how they are being run next year.
The warning follows a study to be published today on the monitoring of the sewerage plants in 2002 and 2003, the Urban Waste Water Report, which found that 76 per cent of small and medium-sized plants were not meeting minimum standards.
The compliance rate for larger plants was higher, but half were still failing to meet basic standards.
The study found that contamination levels from the water discharges to exceed national limits in a number of cases, while many plants had failed to take adequate measurements of the discharge levels.
The report did highlight that record investment in waste treatment plants was beginning to make a direct impact.
In 2003, 58 per cent of waste water received secondary treatment, up from 29 per cent in 2001.
The rise was in part caused by the opening of treatment plants in Dublin and Cork, at a cost of more than €400 million.
The EPA's Office of Environmental Enforcement warned that it would take enforcement action against councils to ensure they "address problems identified in the report".
The office said it was "concerned about the ongoing management and operation of many of these facilities, particularly about the low level of compliance being achieved at urban waste water treatment plants around the country"
The office also served 10 statutory notices during 2004 on local authorities for mis-management of waterworks sludge, from the treatment plants, which is usually land filled or used as an agricultural fertiliser.