Chemists have been flown in from the UK to solve the treatment issue that is crippling water supplies to the capital.

LARGE families with children face being discriminated against under the new water-charging regime.

The state body tasked with running the water system and the minister in charge of it are locked in dispute over how much free water will be given to families.

The system favoured by the operator is one solely based on the size of the house – rather than the number of people living in it.

Under this system, a family of two adults and three children living in a three-bedroom, semi-detached home would get the same free water allowance as a single person living next door. But the family would obviously be using far more water and therefore paying more per head.

When water charges come into effect in 2015, a free allowance will be granted first, then charges will apply for amounts used above and beyond that.

A heated row between Irish Water and Environment Minister Phil Hogan centres on whether the amount of free water allocated should be based simply on the size of the house, or on the number of people living there.

Irish Water wants the allocation to be calculated based on house size, arguing this is the only feasible way to operate the system.

All houses of a particular size would therefore receive the same allowance, as the number of bedrooms would be taken as an indicator of how many people were living in the house.

But Mr Hogan wants the allowance to be based on the number of people in the house to avoid penalising families with children. It is understood the minister feels Irish Water's plan would be unfair to larger families.

The energy regulator will decide by Christmas how the system will operate. But government sources say Irish Water is pushing for house size to be the sole factor.

"Irish Water and Bord Gais want it to be on the house – typical engineers' solution. Phil (Mr Hogan) wants it on the number of people in the house. It's still being looked at. It has to be worked out," a government source said.

But sources in the water sector say the row is a distraction.

"There's no such thing as free allowances. If you get the first batch free, you just end up paying more for the rest.

"It kind of doesn't matter to Irish Water. They'll have to take it whatever way it works out. It can be done but it is administratively more difficult. How do you police it?" a source asked.

Water charges are coming into effect from October 2014, but the first bills will not land until January 2015.

Homeowners will have to pay a standing charge for the metering system and will receive a free allowance of water to give them a very basic supply.

Any use above that amount will be charged at a rate yet to be determined.

Householders who refuse to pay will not be cut off, but are likely to see a severe reduction in pressure, meaning they cannot use dishwashers, washing machines, baths or showers.

Enough water will be provided only for drinking purposes.

Based on the experience in Scotland, which operates a similar system, the average bills are likely to be between €300 and €350 for a family.

The average person uses 145 litres a day, most of which goes on flushing the toilet, washing machines and showers.

However, the free allowance is expected to be only a portion of this amount.

The small free allowance means it will be next to impossible to avoid a bill.

The regulator, the Commission for Energy Regulation, is currently devising a system on how charges will be introduced.

The country's leading economic think-tank, the ESRI, is finalising a report on the issue of affordability and regulation measures.

The regulator will have to take into account the cost of producing, treating and supplying water and the investment needed to upgrade and maintain the network to internationally accepted standards.

The Government will provide a certain level of funding for upgrades over the coming years, but Irish Water will then be expected to pay for upgrades.

Only when the regulator has calculated annual costs will a final decision be made on how much each homeowner is expected to pay.

One hundred and fifty five water plants need to be upgraded, serving a population of almost one million people.

More than 280,000 homeowners are served from supplies which will not be upgraded until 2022 – seven years after the introduction of charges.

It is not yet clear if people living in affected areas will be exempt from charges and if they will be refunded in the event of a problem with their supply.

By Fionnan Sheahan and Paul Melia

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Irish Independent