Up to 70,000 households could face bills of up to €500 if Irish Water is allowed to charge people for wasting water.
The Commission for the Regulation of Utilities will make a decision on the proposal by the end of the month.
Irish Water is suggesting a charge of €1.85 for every 1,000 litres used above the normal allocation, with the charge to capped.
Solidarity TD for Dublin South West Paul Murphy said people will be back on the streets if it goes ahead:
"I think there would be very substantial protests. One are a of protests would be important is the general election.
"Originally this scheme was meant to come in to effect in January of this year. It's now being put off until next year because of the fact that the local elections and European elections were happening, but the same will apply in terms of the general elections."
