Irish Water has insisted that all contracts awarded are in line with European rules on public competition.
As the state monopoly faces calls to explain how it spent 50 million euro on external consultants, it has also been forced to clarify that IT companies were hired under strict guidelines.
Parent company Bord Gais said it and Irish Water had been scrupulous in the awarding of contracts.
"To ensure value for money and transparency, all contracts have been awarded in line with the guidelines set out at EU level for public sector procurement," it said in a statement.
It claimed it has saved 58 million euro in software licences by using the same IT systems and processes as Bord Gais for billing, asset management and utility financial systems.
The denial was issued following reports that four contracts were awarded by Irish Water for IT services without being put out to public competition.
"The procurement of software licences with Bord Gais was subject to a full competitive tender process," the company said.
"In instances where Bord Gais needed to extend the application of these software licences beyond the stated application in the initial competitive tender, Bord Gais adhered fully to EU rules in negotiating software licence extensions to Irish Water."
Bord Gais published notices in the EU journal on the contracts in accordance with EU procurement rules, it said.
"Both Irish Water and Bord Gais strongly reject any suggestion that the company was not fully compliant with all procurement rules," it said.
The head of Irish Water, John Tierney, is to be questioned by the Oireachtas Committee on the Environment, Culture and the Gaeltacht this afternoon before the Public Accounts Committee takes the company to task over the spend on consultants.