The testing is carried out by The Drug Detection Agency.
It is one of the only tertiary providers in the country to conduct compulsory drug testing of its students and has disclaimers about the testing on all the advertisements for trades courses.
Waiariki engineering technologies and construction head of department John Kelly said while the compulsory drug testing undoubtedly had impacted on enrolments, it was not the only cause.
"If we stopped doing the drug testing, absolutely our enrolments would change, but by how much? It's hard to say. Things like the merger and a declining unemployment rate are also contributing to this year's low enrolment numbers."
He said enrolments for semester two this year were also looking "flat".
"We have been sending the message out that we are doing compulsory drug testing and we try to make sure that is understood during the student's first contact with us. Generally they're pretty up front and we try to make it clear the testing's not about judging, it's about the environment we want them learning in and making them more employable."
Of those students who did submit to the testing, 16 (across all four campuses) produced 'non-negative' (positive for drugs) results.
A total of 239 students were enrolled in trade qualifications for semester one, 2016.
"We think the initiative is still in a 'bedding-in' phase. We want students to know there are strict conditions and the drug testing is not going away but there is still a misunderstanding there," Mr Kelly said.
"The reality is, drug testing will be a part of their world with trade businesses doing workplace testing so those put off by our drug testing were likely not going to be students studying for the right reasons."
Mr Kelly said about 95 per cent of the positive results were for THC (cannabis).
Those who test positive for drugs are stood down immediately for a week before they can submit, at their own expense, to another test.
If that test comes up positive, they cannot continue with that semester's course, but are not prevented from re-applying further down the track, once drug-free.
Feedback from industry leaders and parents had been overwhelmingly positive, Mr Kelly said.
"Employers and the parents of other students are over the moon we're doing this. Yes, enrolments are down but the positives far outweigh the negatives. Other polytechnics are very interested in what we are doing as well - all eyes are on us as this rolls out.
"At the end of the day, if we can give students a reason to stop doing drugs, they just might."
The Drug Detection Agency Rotorua branch general manager Errol Brain said the percentage of positive test results at Waiariki was "just a fraction" above national averages in workplaces for 2015.
"We are going into workplaces in the trades industry already and have heard really positive responses about Waiariki's decision to drug test students.
"For those in these industries, drug testing is the norm and students need to be prepared for that. Waiariki has done a good job in making sure it's been an informed process and made it clear it's not about catching people out, it's about health and safety."
He said there were a few other tertiary providers who did submit students to compulsory drug testing, but could not reveal which ones for privacy reasons.
Tradestaff central North Island regional manager Geoff Campbell said there was an increasing expectation from industry to have employees "willing and confident to take a drug test".
"Drug testing is a standard procedure at Tradestaff and is openly discussed as it is a reality of industrial trades."
Mr Campbell said he was aware of trade institutes conducting drug testing and said it was important for those institutes to align with industry practises and expectations.
Tissink Builders owner Roland Tissink said compulsory testing at a student level was a good idea.
"To be fair I don't see a lot of drug use, not in residential building, but it definitely would make me feel more confident about hiring somebody knowing they had passed a drug test during their course."
