The country's largest landlord is racing to keep up with the number of tenants using and making P in its houses in Northland.
Housing New Zealand spent $231,361 decontaminating 13 Northland houses infected by methamphetamine over the past three years, but that figure would rise now that HNZ would start testing its houses each time there was a change in tenant.
Whangarei tenancy manager Cheryll Voullaire had a 286-property portfolio across Onerahi and central Whangarei and said it was frustrating when families had to wait while a property was decontaminated.
"Meth has really just come to the surface in a hurry. We're finding out more and more about it all the time."
Dying vegetation around drains, stained sinks, headaches and stinging eyes when visiting properties were red flags for tenancy managers.
HNZ spokesman Gez Johns said narrowing down who was responsible was complicated, as contamination could spread even by moving in furniture that came from a meth-infested environment. This made prosecuting tenants difficult.
"Remediation could require a triple wash of the decontaminated area and/or a strip-out of linings, fixtures and fittings," he said.
The Ministry of Health's "safe guideline" for meth levels was 0.5 micrograms per 1sqm and houses were retested after decontamination to ensure they complied. In the past, HNZ commissioned testing when use or production was suspected, but it was now moving towards testing houses whenever a tenant moved out.
MethSolutions director Miles Stratford was not among HNZ's decontamination contractors, but felt the state housing provider could be doing more to stop meth-contaminated homes going into the hands of unsuspecting private buyers.
He estimated about half the HNZ homes his company tested at the point of sale were positive for meth.
"The biggest concern is getting a property where there's been manufacture - you get a wide range of toxic chemicals," Mr Stratford said.
"A little bit of meth from use in the house shouldn't be a profound health and safety issue. But for some people it's a bit like someone's died and it's enough to put them off. If you've got houses with meth in that's indicative of meth-related behaviour which some people don't like."
Mr Stratford said of 167 private properties it tested in Northland last year, 94 had traces of methamphetamine - or 56 per cent. Whangarei had the highest rate of positive results in the country.
Mr Johns said HNZ was taking a "leading role" tackling the meth issue and only sold a handful of properties each year in Northland.
"Obviously we wouldn't knowingly look to sell a contaminated property without full disclosure to prospective purchasers ... as we have begun to better understand the potential contamination effects of P use, we have moved to testing all properties at the end of a tenancy. This should pro-vide greater levels of confidence for the next occupants."
HNZ sold 15 Northland properties in 2014, potting $2,098,000.