City council chief executive Sue Bidrose said the injuries happened about 18 months ago as users crossed joins in the slide.
While the injuries were minor, council staff had added a new gel surface to the slide.
However, it was only a temporary fix, she said.
The explanation came after Cr Aaron Hawkins asked about the $4 million plan to renew the slide, an issue that had not come before the council until it turned up in the draft 10-year plan.
Parks and recreation operations manager Jendi Paterson said staff assessed the hydroslide during the last year.
``It's been at Moana Pool for 33 years, and is suffering from quite bad osmosis.
That meant the fibreglass was coming away from the frame.
``It is past its useful life.''
Cr Aaron Hawkins asked about the timing, and was told the new slide was expected to be installed in the 2019-20 year.
Ms Paterson said the pool was mitigating any danger by regularly adding the gel surface to the slide.
``It is still able to be used but that is a short-term fix.''
Ms Paterson said the slide brought in about $175,000 of revenue each year.
She said staff were scoping a design for the new slide.
