The free water allowance initially set for children is being cut by 17,000 litres.
It had been suggested in May that children would receive a free allocation of up to 104 litres each day, the equivalent of 38,000 litres a year.
The Commission for Energy Regulation today confirmed proposed charges of half a cent for every litre of water used.
A household with one adult will pay an average annual charge of €176 For the supply of water and the handling of the home's waste water, rising to €278 if two adults live there, €380 for three adults, €482 for four and €584 for five.
The charges will be capped at these rates until March 2015, after which those with meters installed will pay based on consumption.
The charges will only apply to adults, with the Government funding the cost of providing water for children.
However, Commissioner with the CER Paul McGowan admitted that the free allowance for children had been reduced.
"The Government had previously advised the child allowance would be 38,000 litres, but they had said (that was) subject to verifying that number," he said.
"The analysis Irish Water carried out and we have looked at indicates children do not consume 38,000 litres. They actually consume 21,000 litres."
In documents published today, the CER said: "Allowances should be split into four equal parts to allow even distribution of the allowance over a 12-month period. Any units not used within one quarter may be carried over within the 12 months from the date which it commenced.
"No units may be carried over into the next 12-month period. The first allowance period will begin on 01 October 2014."