The National Drug Intelligence Bureau's latest wastewater testing showed the levels of meth and ecstasy are higher in Christchurch than in Auckland.
However, Newbold believed test methods would need to be scrutinized before figures could be validated.
"You need to know where they tested and how they chose the water they tested. How did they choose certain areas above other areas? Wastewater's everywhere. Some places would have high levels of meth, other places would have low. "
"You'd need to know the testing methods - the police are notoriously bad for these kinds of things, they're not scientific," Newbold said.
The National Drug Intelligence Bureau is a joint operation of the New Zealand Customs Service, the Ministry of Health and the New Zealand Police.
The $220,000 wastewater pilot programme had taken wastewater from the Christchurch and Auckland Rosedale treatment plants and tested for a variety of drugs, including methamphetamine (meth) and ecstasy, on a monthly basis.
Newbold expected the influx of organised gangs in Christchurch would have increased the amount of meth available, but believed market prices were the best indicators of local drug use.
"It's always been the case that drugs are more expensive in Christchurch because they're more difficult to get. If the price in Christchurch has gone down, that's a better indicator of what the availability is like."
He said a gram of meth cost $600 to $700 in Auckland, whereas it cost $900 to $1000 in Christchurch, was lower quality and harder to obtain.
"If the price goes down, it means there's more meth available. If the price goes up, it's a drought," Newbold said.
He did not believe Christchurch would have a higher use of meth than Auckland, despite what the wastewater tests showed.
The aim of the wastewater pilot project was to provide information mainly to police regarding targets such as: treatment and enforcement strategies and measuring the effectiveness of education programmes.
The pilot programme began in December 2016 and water would be tested every month.