The Prime Minister's Chief Science Adviser says he cannot see the point in testing homes for methamphetamine because the risk to health is so low in most cases.
Professor Sir Peter Gluckman has produced a report for Housing Minister Phil Twyford which says there is no evidence that third-hand exposure from methamphetamine smoking causes adverse health effects.
Gluckman said people were more at risk from mould in their home than they were from meth contamination.
"In terms of the housing estate, mould is far more dangerous that meth."
The report has found that remediation in most cases is needed only in homes that have been former clan labs producing the drugs and where meth has been heavily used.
"I can't see the point of testing, full stop, unless the police or the forensics suspect it has been a place of synthesis," Gluckman said today.
His report says that levels that exceed the current standard of 1.5mcg/100cm2 should not signal a health risk and exposure 10 times higher (15mcg/100cm2) would also be unlikely to have any adverse effects.
Because the risk is so low, testing is not warranted in most cases, the report said.
That will come as a relief for homeowners and rental property owners who worry their houses have previously had meth use.
It also means that hundreds of tenants in private rentals and social housing may have been penalised needlessly for the cost of remediation following positive meth tests.
It could also spell the end of the meth-testing industry, which has grown in recent years as alarm has over the effects of third-hand meth exposure.
As an example, Gluckman said he would be comfortable with a level of "several hundred micrograms" in an area where small children would be exposed.
"We're looking at a thousand-fold safety factor in our recommendations, for a naked toddler crawling around the floor licking every bit of the floor up for several hours a day. That's the kind of calculation that's been done, taking it as far as you can."
He said that the power of suggestion could be enough for people to feel ill from the effects of living in a meth-contaminated home.
"There are other things in those houses that are more likely to be causing symptoms.
"You'll start to automatically link that low level to your psychology, your biology."
Twyford said he commissioned the report because of the anxiety about meth contamination and the testing and remediation industry that had grown as a result.
"There has been a widely held perception that the presence of even low levels of meth residue in a house poses a health risk to occupants. As a result, remediation to eliminate contamination has been an extremely costly business for landlords and an upheaval for tenants being evicted at short notice.
"No one is underplaying the social damage caused by meth, but there should be a scientific basis for what are acceptable levels of meth in the current New Zealand context; and remediation of houses should be proportional to the established health risks."
He said the new regime would make 200 previously unsafe Housing New Zealand houses available shortly and save HNZ around $30 million a year in testing and remediation.
NZ Drug Foundation executive director Ross Bell said the panic around exposure to third-hand methamphetamine had grown out of all proportion to the actual risks.
"The message that testing is only warranted in very few cases needs to reach every Kiwi homeowner, landlord, tenant and social housing provider. When this report sinks in, we can expect to see demand for testing to drop right away," he said.
"Since this shameless testing industry took hold, Housing NZ alone has spent $100 million over four years for testing and remediation, evicted countless tenants and had properties sitting vacant.
"This has caused unnecessary distress to tens of thousands of tenants in public and private housing, and led to a scandalous waste of money. We never understood why the previous government allowed this situation to get so out of hand."
As well as evicting tenants, the Tenancy Tribunal awarded costs against some very vulnerable people for "contaminating" their rental home.
"With the basis of 'contamination' now being shown to be bogus, this calls into question the validity of the tribunal findings. The Drug Foundation is calling for financial relief for tenants unfairly penalised by an eviction or remedial costs," Bell said.
Twyford said the report, along with the 1.5mcg/100cm2 clean-up standard (NZS 8510: 2017), would contribute to any regulations that may be made under the Residential Tenancies Amendment Bill (No 2), soon to have its second reading in the House.
He expected there to be public consultation document on meth regulations later this year.