A series of reports for Government has questioned the value of spending tens of millions of euro in State and EU funding on sewage and waste-water schemes in the 1990s.
The reports identified that €248 million was spent on 27 waste-water treatment schemes, yet only a limited number of the projects resulted in any significant environmental improvement to date.
A further €200 million spent on 27 water conservation and public water schemes did provide value for money.
Despite the spending of nearly €450 million, no studies had been carried out on the public and environmental benefits of the projects before they were approved.
The studies also found that there were significant cost overruns, with one project costing nearly three times its original budget.
The highest cost overrun was for two water-supply projects in Monaghan, which cost €15.64 million, 2.7 times the original estimated cost of €5.8 million.
These figures do not account for construction inflation, which was extremely high during the late 1990s when the plants were being built.
The reports, by Mr John Lawlor and Mr Colm McCarthy of DKM Economic Consultants, on 54 water projects that received European cohesion funds during the 1990s, carried out an economic cost-benefit analysis on the schemes, by attaching a "monetary" value to environmental and other improvements from the schemes.
They found that most of the waste-water schemes "appeared to have been poor value".
In 11 out of the 27 waste-water projects, there had been no improvement in the water quality of nearby rivers and lakes after they began operation. There were insufficient data on a further six projects to establish whether there was an improvement, and no data at all on two projects.
Specifically, they found a poor environmental rate of return for the €65 million Dundalk scheme, which also ended up at double its original cost estimate.
Seven projects to clean waste water flowing into Lough Ree, at a cost of €34 million, were found to have an overall negative return, although some individual schemes had a positive return within this.
Three major sewage and waste-water treatment plants in Trim and Navan, costing €45.7 million, also generated limited environmental benefits compared with the cost.
Mr McCarthy, one of the report's authors, said the findings raised questions about the lack of analysis. He said the problem centred on EU legislation that required the construction of many of the plants to comply with new emission limits for waste water, rather than limits for the lakes, streams and estuaries into which that water was being discharged.
"You could end up spending billions and you don't get the bang for your buck we thought we'd get ecologically, and that's what's worrying," Mr McCarthy told a conference organised by the Economic and Social Research Institute (ESRI) yesterday.
One of the country's top environmental economists also suggested a new levy for spreading excessive levels of fertiliser. Ms Sue Scott, head of the ESRI's environmental policy research centre, said VAT returns from farmers could be used, with a little additional information, to calculate which farmers were spreading excessive slurry.