The initial estimated cost of €431 million for water metering was based on the best available information at the time, Minister for the Environment Alan Kelly told the Dáil.

He was replying to Sinn Féin spokesman Brian Stanley, who asked why the cost had increased to €539 million.

Mr Kelly said the initial estimate was based on data relating to non-domestic usage.

“It is not entirely accurate to suggest there was a big jump from €431 million to €539 million in a short period. While that figure was cited a number of times in the months prior to completion of the tendering process, it was the last estimate available.’’

Mr Stanley said the estimated cost of installing meters had increased by 20 per cent. That represented a huge proportion of the taxpayer and public money that had been soaked up thus far by Irish Water for the metering programme. "I must assume that the consultants who came up with this estimate were the same people who were paid €85 million last year. There is considerable anger about that.''

He said a survey by local authorities, which would have been more accurate, came up with a figure of €539 million.

He asked whether Mr Kelly found it “unusual’’ that the figure happened to correspond with the estimated cost of the contracts for installing the meters arrived at six months earlier. Mr Kelly repeated that the initial figure was an estimate arrived at a long time before the tendering process.