Around 80,000 households will be subjected to excessive usage water charges when the new charging scheme is implemented in 2020.
In a report sent to Government last week, the State's water agency estimated it would collect €7m in charges in the first year under the new system.
This will increase to €9m annually within five years, according to the Irish Water strategic funding plan.
In total, the water utility expects to raise €39m over the next five years from excessive usage charges.
The figures are based on between 75,000 and 80,000 households paying the average capped domestic water rate of €260-a-year.
The strategic funding also estimates the cost of running Irish Water up to 2024 will be €11bn.
The new charging system was agreed by Fine Gael and Fianna Fail as part of the confidence and supply agreement which underpins the Government.
Under the agreement, water charges were abolished but - to ensure the country does not incur EU-imposed financial penalties - fines for excessive water use were introduced.
Families using 1.7 times the average - 213,000 litres for a four-person household and 79,900 litres for a single-occupant home - will be forced to pay water charges.
It was previously estimated around 7pc of customers - or 95,000 households - will be hit with excessive usage charges.
An Irish Water spokesperson said the figures were "adjusted for average rates of payment and minus the expected level of customer engagement to rectify the excess use".
"Irish Water recently made a submission to our economic regulator, the Commission for Regulation of Utilities (CRU), on the potential rates for those average households who are using in excess of 213,000 litres of water per year," they said.
"The details of any charges and their application will be determined by the CRU.
Irish Water have estimated the revenue that could potentially be raised if those customers we engage with fail to fix leaks or fail to curb their excess usage."
Estimates were based on the original charging regime.