In its response, the council said it was publishing the figure in the interests of public transparency and having sought and obtained the agreement of other parties to the case.
"Further details of the settlement remain confidential."
The suit began after the council issued a notation against the $46m building's property file after one apartment owner successfully settled out of court with the council.
The notation, discovered in early 2016, read the council was aware of "defects" in one apartment and there could be defects in all apartments.
Cayman Apartments body corporate chairman Paul Clark said yesterday it had taken five years to get to this point, and had cost owners and the body corporate around $5.5m.
"This is what the ratepayers have to pay to battle their council."
He said the owners' and council's costs combined - $7m - would have been a "useful start" to putting right the issues with the building "if the parties had been able to sit down and talk at the beginning of all this".
"That's money wasted as far as the participants are concerned. It's the experts and the lawyers who benefit."
He said owners were considering their individual options for what to do next.
The council's bill relating to the case included $666,026 in legal costs and $868,522 in expert costs, excluding GST.
The $21m settlement was nearly seven times the $3.05m the council has paid out in leaky building claims over the past six years.
And with the council involved in five active leaky building cases currently before the courts or the Weathertight Tribunal - including other apartment buildings - there could be more to come.
The cases included Mount Maunganui's Tayside, The Pacific and Quayside Apartments.
Council corporate services manage Paul Davidson said leaky buildings were a national problem, and councils all over the country were facing historical issues with liability.
"Given that a number of other claims are still active, there is potential for further settlements to occur."
Since 2014, the council has paid out $3.05m for 13 claims, racked up $4.015m in legal costs.
It has paid a further $6.19m to the Department of Building and Housing and the Ministry of Business, Innovation and Employment as part of the Financial Assistance Package for leaky homes.
Under the scheme, the Government paid 25 per cent of the cost to repair a leaky home and local authorities that signed off the original work would pay another 25 per cent.
Active cases
Tauranga City Council has five active weathertight home cases before the courts or the Weathertight Homes Tribunal.
Tayside Apartments
Address: 154 Marine Parade, Mount Maunganui.
Claimants: 8 - the body corporate, 5 residential owners and two commercial owners.
Status: Amended claim to be filed and a hearing date set July 2021.
The Pacific Apartments
Address: 8 Maunganui Rd, Mount Maunganui.
Claimants: 55 - the body corporate and 54 owners.
Status: On hold until repairs completed, hearing after January 2022 once repairs complete.
Quayside Apartments
Address: 28 The Mall, Mount Maunganui.
Claimants: 1 - the body corporate.
Status: Before the Weathertight Homes Tribunal, on hold until repairs completed.
19 Grove Ave, Mount Maunganui
Claimants: 1 claimant.
Status: Initial stages of litigation – council's defence filed in December 2019, in process of joining third parties.
85 Osprey Drive, Welcome Bay and 170 Windermere Drive, Poike
Plaintiffs: 4 plaintiffs brought claim and represent another 32 plaintiffs.
Status: First stage hearing in 2020 which the council is not involved in.
Source: Tauranga City Council
