Former Irish Water boss John Tierney from Terryglass, received a retirement package worth a total of €573,000 when he left the State body in April 2016.
The figure is included in the agency's 2016 annual report which was published this week.
Mr Tierney's package was made up of a €100,000 severence payment and €473,000 in defined pension contributions.
His total payments from January to April 28, 2016 came to €655,000, which consisted of €67,000 in basic salary for the four months; €473,000 in defined pension contribution; €100,000 in termination benefits / severence; €11,000 in pension contributions and €4,000 in other benefits, including company car and health insurance.
The former Dublin city manager, who worked in local government for 36 years before joining Irish Water, was paid a €200,000 annual salary when he was appointed by then Minister for the Environment Phil Hogan in January 2013 on a three-year contract.
At the time of his retirement, Irish Water said that Mr Tierney would have been entitled to a similar package upon retirement from the local authority.
Irish Water stated that Mr Tierney "carried his full service to his new employer and, in line with Government guidelines regarding the transfer of staff from local authorities to Irish Water, his retirement arrangements are exactly the same terms that would have applied had he retired as Dublin city manager".