Update 9.36pm: The Green Party leader believes some people will not want their refund from Irish Water.
Almost one million people who paid their charges will receive cash back by the end of the year.
The refunds will cost €173m.
Eamon Ryan thinks a system should be set up for those customers who believe the cash should go to Irish Water.
"We could well set up a system where people could say 'I don't need that, take that money back. I'd prefer if you invested in water infrastructure," said Mr Ryan.
He suggested that a special account could be set up that targets pollution in the worst places.
"That's the kind of approach we should take because I think a lot of people are going to look at this back, I want to invest in water," he added.
Earlier: Just under a million households will receive a "cheque in the post" from Irish Water by the end of the year.
The Government has approved a refund scheme which it says will mean most households will not have to do anything to get their money, although those who have moved home will have to get in touch.
The refunds will cost €173m, the administration will cost €5m and Irish Water will need €114m to operate in place of charges this year.
Minister Eoghan Murphy says he and Fine Gael believe in paying for water, but this had to be done in order to have a government.
He said: "We'd rather not do that, we believe that there should be a consistent funding stream for domestic water customers and users into Irish Water. Not just for conservation purposes, but also because it makes sense economically.
"We can't do that now. I think over the coming weeks as we approach the budget you are going to hear politicians talking about spending extra money in different areas.
"Those same politicians made a decision and forced us into this position to cut off this funding stream, which we didn't want to do."
Minister Murphy said it is expected all 990,000 customers will be refunded before the end of the year.
Irish Water is to run an information campaign that will inform customers on the next steps.
A household of two adults who paid all five water bills will be due a refund of around €325. A single adult household who paid all five bills will be due €200.
Payments were made by homeowners to Irish Water between late 2015 and 2016, before charges were suspended.
Meanwhile the Water Conservation Grant is unaffected.
The Department of Housing, Planning and Local Government says this was a standalone, separate grant for all households - whether Irish Water customers or not.
"Its aim was to support conservation in the home and was distinct from domestic water charges. Therefore, the grant is not being deducted from refunds."