A spokesperson for Irish Water says there's been a spike in the numbers registering their households in the last few days.
The company is urging people to register by the deadline of midnight tomorrow.
However they also said they would continue to accept registrations after the second of February.
Yesterday, an estimated 40,000 people took part in protests against water charges across the country, over half of them turning out at a major rally in Dublin.
But figures from Irish Water show that thousands more are quietly registering with the company ahead of tomorrow's deadline.
As of Friday evening, more than 830,000 had signed up to Irish Water - over half their customer base of 1.5 million households.
The company will issue fresh figures tomorrow morning, which will reveal the numbers registering at the last minute.
Irish Water says the deadline is to ensure that people are eligible to apply for the Water Conservation Grant.
They also say registration will ensure more accurate charges when billing begins in April.
Householders who aren't registered will automatically be charged the default bill for two adults of €260.
