A so-called grey market in dodgy building products is being investigated by the Ministry of Business, Innovation and Employment (MBIE).
But two Aucklanders who train plumbers and council inspectors said they doubted it would make any difference, saying New Zealand was a dumping ground because the rules were weak.
Darren Waith and Bill Wright both estimated half of the new homes being built here had plumbing in them that would be banned in Australia.
Mr Waith chairs the National Plumbing and Pipelaying Standards Committee - which could be considered ironic, because he said there were no legally enforceable standards in New Zealand, and that was having a predictable result.
"Dumping. An easy dumping ground for product," he said.
"It is not illegal - it's not illegal to install them, it's not illegal to import them or sell them. You cannot dump the product into Australia - everything must comply with their standards, which is their WaterMark."
Both men said it mattered, because bad plumbing was a health and pollution risk.
"Say, for example, a brass fitting - these are the fittings that go behind the wall, you don't see them," Mr Waith said.
"What say that brass fitting's full of lead and lead leaches into the water? An inspector can't test that brass fitting, it's impossible. And there's no standard for them to recognise and measure it against."
He estimated about half of new houses in New Zealand had plumbing products in them that would fail Australia's performance standards.
Mr Wright, an ex-plumber turned consultant who works helping two dozen councils, including Auckland's, keep their building inspections up to scratch, agreed.
"It's prolific across the whole industry. There's non-compliant plumbing product from the point of connection to the boundary, if you are talking about a water supply, right through to the point of connection of the foul water drain," he said.
"At least 50 percent of new houses have a non-compliant plumbing product in it."
Home Owners and Buyers Association president John Gray told Morning Report consumers and workers were the ones who ended up losing money, and the issue was getting worse.
"It is a fairly widespread problem in terms of the poor quality of copper piping, but it strikes at the real issue - being that there is no standard upon which these products are tested."
Mr Gray said he had also had reports of shower glass being imported that was not safety glass.
'No standard to comply with'
Mr Waith said he wouldn't even use the term "non-compliant" to refer to sub-standard products, as there was no standard to comply with.
"The Building Code is about 20 years out of date," he said.
"Although we are trying desperately to get the Ministry of Business and Innovation to update it and get some subject experts from our industry, they just refuse to listen. And I think a lot of it's around monetary concerns."
The cost of monitoring and enforcing standards would be daunting, and the industry's expectations that regulators would grasp that nettle was low.
The Plumbing Distributors Association went to the Commerce Commission recently when, as a test, it went around a dozen or so Auckland plumbing outlets and found about half of them selling shower glass and taps that were not up to scratch.
The commission warned eight shops about failing to display water efficiency labels; seven fixed that, and one didn't and was fined $2000.
MBIE, meanwhile, recently looked into one supplier's claims another was selling non-compliant products, but found no evidence of that.
It did, however, uncover something else.
"The investigation did raise concerns around the availability of plumbing fittings supplied directly by small-scale importers without documentation to support code compliance," MBIE, which did not make anyone available to interview, said in a statement.
"The scale of this activity and the actual quality of the products are not yet known, nor is it limited solely to plumbing products."
The ministry was still investigating the matter.
MBIE has never used the powers it has to ban building products. Instead, it favours educating importers, getting consumers to pressure plumbers and telling local councils to do the enforcement.
That is unlikely to be enough as more and more imported product comes in, some of it from migrant tradespeople who have realised it is relatively open slather here for non-certified products from their native countries.
Mr Wright said one solution could be for the government to make a system called CodeMark mandatory - it's a certification scheme for all building products but, at the moment, it's voluntary.
The Master Plumbers Association said the only way to fix the issue was to adopt mandatory quality assessments before any pipes and other plumbing fittings could be sold, as happens with Australia's Watermark system.
Chief executive Greg Wallace said otherwise there could be no assurance that pipes being fitted now would not fail in large numbers in future.
"Master plumbers don't want to put extra regulation on an already highly-regulated system. But we also don't want someone turning up to us in five or 10 years with a leaky home situation, like we currently have in New Zealand."
Mr Wallace said greater checking of fittings now would be more expensive, but could save money in the long run.