The Herald can reveal that only around 171,000 households registered after the reduced price structures were announced by the Government on November 20.
Irish Water has claimed that 1.04 million households have now “validated their info”.
But it said that only 79pc of that figure, or 821,600, were on the public water mains and are considered customers of the semi-state.
The utility estimates that around 1.5 million households across the country are on the public network, meaning that in the region of 678,400 of those have not registered.
The figures will make for some grim reading for the Government, which had hoped the new charges would encourage people to supply their details to the embattled company.
By the end of the first week of November, when higher charges were still being proposed, 828,000 homes had validated their information with Irish Water.