Thousands of people are expected to apply for the €100 water conservation grant by midnight.
The deadline was extended by two weeks on October 8th, after high volumes of calls and issues around the postal delays arose on the day.
Almost 54,000 people made applications that day and 41,947 applications have been submitted since.
The latest figures show about 66 per cent (857,769) of the households that the Department of Social Protection sent 1.3 million letters to in June have applied for the grant.
The department said it has paid the grant to 810,000 households.
To apply for the grant, people who are customers of Irish Water do not need to have paid their water charges bill.
Anti-Austerity Alliance TD Paul Murphy said Irish Water needed to be fully transparent about the number of customers who have paid their bill.
Mr Murphy told RTÉ's Morning Ireland he believed people had been "bullied" into paying water charges.
“The reality is that this is a company who can’t even give away €100. They had to extend the deadline after saying they wouldn’t again. It just shows the level of opposition that exists to Irish Water. It will be reflected in the election campaign,” he said.
A spokesman for Minister for Environment Alan Kelly said the deadline was “not expected to be extended at the moment”.
He said eligibility for the grant was not connected to the payment of bills and there was “no suggestion” the rules would be changed for next year.
Irish Water said their figures showed 55 per cent of its full customer base are now paying their bills.
Grants can be applied for online at watergrant.ie or calling 1890 100 043 or 0761 087 890.
What you need to apply for the grant:
-Transaction Identification Number (TIN)
-Water Point Reference Number (WPRN)
- Personal Public Service Number (PPSN)
- Bank or other financial institution account details