City council voted unanimously Monday night to go ahead with a referendum on the issue, despite a city clerk's office ruling last week that there weren't sufficient signatures on a petition calling for a vote.
Mayor Michael Fougere made the motion for the referendum, and told reporters before the meeting that it was needed because there was clearly a desire for the public to have its say.
Regina Water Watch spent a month collecting signatures to try and trigger a binding vote on the $224-million project.
But on Friday, the City Clerk declared the petition was not valid because too many people left required information off the document when they signed it.
Fougere said that he expected a referendum will cost in the range of $200,000 to $400,000.
It's not clear when a vote may be scheduled.