"There really does need to be a mandatory system that ensures rentals are warm, safe and dry, in the same way that a cafe owner needs to get a health rating from the council to sell food that comes out of their kitchen," Lenihan-Ikin said.
"Last year we ran a campaign in the local elections, and a majority of elected councillors signed a pledge to introduce a mandatory WOF.
"So we're still hoping for the mandatory WOF within the next three years, in this council term."
Lenihan-Ikin said bad housing had a huge snowball effect.
"We see students every day who are getting sick from cold, mouldy flats.
"Once you get sick in the winter, students have to stay home from class, spend money they don't have on health care, get behind on assignments, stress builds up."
Renters United spokesman Robert Whitaker agreed it was a good first step, but that it ultimately needed to be mandatory.
"Good landlords who have good high-quality properties will probably be keen to take part in a voluntary WOF, because they'll be keen to show their property is good.
"But the real need for a warrant of fitness is about improving the properties that don't meet it.
"The only way you're going to meet that is by it being a requirement, rather than an option."
Whitaker said a compulsory WOF system could be brought in after the council trialled the voluntary system, or as a national scheme run by the Government.
"These are really minimum standards. Every house in New Zealand should be meeting them."
But the announcement might not be greeted so warmly by landlords.
Property Investors' Federation executive officer Andrew King said they were against any form of Warrant of Fitness.
"They're an expensive way of bureaucratically checking someone's accommodation."
He said some rental houses weren't of good quality, but there was an issue with "quality of all housing in New Zealand".
"Tenants are not willing to pay for better quality properties with extra features.
"People are living in these houses, and I think they should be free to make their choices as to what condition house they actually live in."
The full details of the scheme are expected to be released at 8.30am today.