The Government is expected to confirm the proposed sale of part of Bord Gáis today.
Minister Pat Rabbitte has been seeking Cabinet approval for new laws which would allow the energy business to be sold.
It is estimated that sale of the business could raise up to €1.5 billion.
Fianna Fail's Michael McGrath said he is concerned that Irish Water, the company set up to control the water system could be affected.
"Part of the reason Irish Water was established in the way that it was - sitting essentially within the family of Bord Gáis as it was - was because of the expertise Bord Gáis energy has in dealing with consumer issues," he said.
"And now, with the sale of Bord Gáis Energy in the open market, we would be very concerned at the future of Irish Water."