The $5.7m brought forward was originally planned for a new pool in 2023.
The councillors had gone to Waterworld on Tuesday to view the work that needed to be done.
Councillor Mark Bunting was pleased that the council was fixing up one of Hamilton's main amenities.
"A few years ago we were sitting pretty with pools, libraries and theatres. We had all the stuff that the councils previously had put in for our generations," Cr Bunting said.
"Unfortunately they kind of all fell to bits at the same time."
"This isn't gold-plated by any means. This is just keeping the thing going."
Councillor Paula Southgate said she did not want to keep heaping costs onto ratepayers but believes that the work needed to be done.
"We were out there and we saw the basic work that needed to be done, so let's just do this," Cr Southgate said.
Councillor Dave Macpherson warned council that Waterworld was a lesson to the council.
"Don't put off today until tomorrow, because that is what happened for the last few years with this council," Cr Macpherson said.
"A pool in a city like Hamilton is vital."
Waterworld joins Gallagher Aquatic centre as one of Hamilton's main swimming facilities, and between them the pools had more than 562,429 visitors.
Waterworld will also be required to undergo earthquake strengthening by 2029.
