Landlords, including local authorities, have been warned that they have just weeks to contact Irish Water with the names of tenants or they may be held liable for all water charges on whatever properties they own.

The utility was forced to issue the warning after it emerged that the numbers registering for the service across the rental sector was significantly less than among owner-occupiers.

While roughly 30 per cent of would-be customers of the utility would be expected to come from rental properties, the number of completed registrations from that sector currently stands at just 17 per cent. The remaining 83 per cent of those who have registered are owner-occupiers.

Irish Water has said it is now in a position to contact landlords directly after being given the green light to act by the Data Protection Commission (DPC).

The utility’s spokeswoman, Elizabeth Arnett, said earlier this month it had been cleared to seek the names of tenants, including those who live in local authority housing. She told The Irish Times the DPC had confirmed that “once we have gone through the processes correctly and allowed all occupants ample time to come forward then we can approach the landlords”.

She stressed that all landlords – including local authorities which control the bulk of the rental market — would be treated the same when it came to billing. If more than one person is named on a lease, it will be up to the landlord to provide the name of just one tenant. Irish Water will then engage directly with the named individual “and provide them with an opportunity to confirm their details”.

Ms Arnett stressed that it would be in tenants’ best interests to contact the utility directly as failure to do so would mean they could not avail of the Government’s €100 water conservation grant. She said single-adult households would also run the risk of being hit with annual bills of €260 instead of €160.

“Landlord and tenants can confirm details at any time. However Irish Water would encourage an early response to ensure details are as accurate as possible in advance of billing,” she said.

She said some 1.22 million of the 1.9 million homes across the State had contacted Irish Water with almost a million responses coming from among the 1.5 million households on the public network, a response rate of two-thirds.