Williams argued the case could boil down to five pages of a report which was written in late 2017 by NCC's projects and design manager, Mark Plested.
He argued the five pages, which recommended council look for a new location, were the catalyst for council moving away from a 50 metre pool development at the current Onekawa site, to the Prebensen Dr 25m pool build.
He described it with a train metaphor: the council changing its tracks and leaving the community at the station.
The report recommended staff look for an alternative site for the aquatic centre, which council staff then did, settling on the Prebensen Dr site, due to contamination at Onekawa.
It was not released to the public, nor provided to councillors prior to them voting, Williams said.
He said in November 2017, ratepayers were told a 50m pool redevelopment would be progressed as through the 2018-2028 long term plan (LTP).
This option had been developed over three years, including with community input through a consultation process which received 2010 submissions, 1695 of whom supported a 50m pool.
He said after a series of emails, initiated by council CEO Wayne Jack, council decided to abandon any 50m pool option as part of the LTP in late March 2018, which Williams said was a "casual" way to make a significant decision.
Council then approved a consultation document on April 10, 2018, with two options, the Prebensen Dr options and an option which would expand existing facilities at Onekawa.
Williams said for a $41 million project, the community was given two pages to explain why the 50m option was not progressed.
He said the consultation process which council relied on was "manifestly inadequate", arguing a "prior engagement" step should have been completed, consulting the community on Prebensen Dr before it was included in the draft LTP.
Of 620 submissions received on the pool as part of the LTP, there was a even split between the Prebensen Dr site and an expansion at Onekawa.
One hundred people also submitted they wanted a 50m pool, despite this not being an option given.
Seven people gave oral submissions as part of the process.
Councillors were advised to disregard information presented during the hearings that was not in written submissions, including as produced in answers to questions from councillors, Williams said.
The hearing continues. It is expected to last until Wednesday.
