These included a locked ground-floor cupboard that contained dangerous levels of sulphur monoxide - just feet away from a council employee's desk.
Mr Williams also gave the less hazardous examples of ageing chairs in the cafeteria and worn carpets as proof of the need for major refurbishment.
"This building is 30 years old and has minimal amounts of expenditure on it...it does need investment," he said.
Some councillors were initially reluctant to commit to an annual spend of $650,000 for the next six years on civic centre upgrades.
But most dissenting voices were silenced by a slideshow of images providing visual proof of some of the more worrying maintenance issues.
Gaping holes in the roofs of toilets and the floors in the building in which they sat appeared to shock councillors present.
Only the smallest laugh was raised by a photo of a hole in the wall that council staff had decorated with a cartoon rat - a tribute to a regular visitor to the building.
Rotorua mayor Steve Chadwick described how a tile had recently fallen from the ceiling in her office, disintegrating on the floor like a "sodden Weet-Bix".
Mrs Chadwick gave her strong support for funding the civic centre maintenance, and stressed the value of the building to the council.
"There isn't much pride in other civic centres."
Council chief financial officer Thomas Colle said previous spending programmes had failed to ensure upkeep of the building.
"Over the years we have squeezed the renewal programme on this," he said.
Councillor Merepeka Raukawa-Tait suggested the examples of maintenance issues shown to councillors could be "just the tip of the iceberg".
Councillor Charles Sturt expressed his frustration the situation had deteriorated to the point where a multimillion-dollar refurbishment was needed.
"We pay staff good money to be top property managers and it's really disappointing to sit here and see this sort of thing," he said.
In the end it was an almost unanimous vote to approve the spending, with only Rob Kent voting against.
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