Customers have to register by June 30 to get water grant
Householders cannot claim the €100 water conservation grant unless they register with Irish Water by June 30.
The Department of Social Protection will not sanction payments beyond this point in a further ratcheting up of pressure on the 500,000 homeowners who have so far failed to register.
It comes as Irish Water has admitted there will be mistakes in bills which are being sent from next month.
It says that details such as the number of people in a household may be incorrect; that 0.5pc of meters, or 2,500, will not be read due to technical difficulties while up to 150,000 properties with a private well and septic tank will be mistakenly billed for services.
The bills will be sent to more than 1.5 million properties from next month.
Around half a million households which have failed to register will receive a 'default' bill of €65 for three months, or €260 per year.
And a significant number of the one million customers who have registered can expect problems with their bills.
The utility said it would have 750 staff in place in its call centre to answer customer queries.
"If there is an issue, call us to clarify," a spokeswoman said. "We want the right bills to go to the right customer, (but) we know the information is not complete. We want to front up at this stage, there will be issues and challenges. The billing system is working, but it's only as good as the information we have. We anticipate a lot of calls on this."
Among the issues are:
Up to 2,500 meters will not be read due to technical difficulties, meaning inac-curate bills will be sent. The regulator has insisted that 98pc of meters must be read, and Irish Water said it expected problems in around 0.5pc of the total.
Homeowners on boil-water notices may also be mistakenly sent a bill for drinking-water. The utility said it would accept that the water was not fit to drink and make the necessary deduction on the next bill.
Bills will be addressed to 'The Occupier' in up to 50,000 metered homes. This is because they have a 'non-unique' address, or one which is shared by a number of other properties, for example in a townland.
An Post allocates a unique number to each property in the country, based on map coordinates, and customers with non-unique addresses will be sent two items of correspondence - a bill which could be, for example, to 'The Occupier, Main Street, Bray', which will include a so-called Water Point Reference Number (WPRN) allocated to the property.
Irish Water will send a second letter using An Post's database, and ask householders to compare the WPRN to that on the bill. This allows them to update their database with correct details.
The first bills will be issued from next month, with around 37,000 to be sent every day. The entire billing cycle will take up to eight weeks, meaning some homeowners will not receive their bill until June.
Irish Water insists that one-in-three homes will have bills below the cap, which stands at €160 per year (€40 for three months) for a single-adult household and €260 (€65) for a home with two or more adults.
The bills are based on meters that were installed by January 1 last, around 500,000 properties. All other homes will be sent an 'assessed' bill. However, if a meter has been installed since January 1, it will be taken into account for the next billing period.
Each household will also receive an information booklet with their bill setting out how the charges work.
Among the "key things to remember" include a decision that the water conservation grant will only be available if households register no later than June 30, it says.
The grant will not be deducted from bills, but paid in a lump sum in September. Customers must apply for the grant through a dedicated website called www.watergrant.ie, using their Irish Water customer account number and other details.
The development comes despite the water regulator extending the deadline to register until December 31. This allows customers to claim their 'free' child's allowance and avoid a default bill, but does not cover the water grant.