Irish Water says over 1.1m households have registered their details with the utility as of this evening, but say that around 600,000 households have yet to do so.

The deadline for registering with Irish Water expires tonight at midnight, but there is no penalty for failing to do so. The utility says there will be nothing blocking new customers registering from tomorrow on, although they will not receive the €100 conservation grant.

Anti-Austerity Alliance TD Paul Murphy says Irish Water are misrepresenting the figures. The AAA say Irish Water are underestimating the number of households in the state who are liable to register with them.

“Less than 50 per cent of their potential customers have registered and this is after two previous extensions of the deadline,” Mr Murphy said.

"Irish Water are understating their potential customer base by 260,000 houses or 15% in order that they can claim that over 50% of households have registered. As with all wars the first casualty is truth and unfortunately despite Irish Waters best attempts to show otherwise these figures prove that they are not telling the truth about their registration rate," Mr Murphy said.

“We’re open for business now for evermore, amen, and it’s normal utility business to be changing customer details at any point,” said Elizabeth Arnett, spokesperson for Irish Water.

The Department of the Environment is urging households to register their details with Irish Water as soon as possible, in order to get the €100 water conservation grant, and to get billed correctly.

Ms Arnett says for anyone who hasn’t registered by now Irish Water “will be applying the sort of standard charge of €260.”

“Those who haven’t confirmed their details will not be eligible to receive the conservation grant of €100 but you can confirm details with us at anytime,” she added.