The 10km sewerage system and airport-based treatment plant, estimated to cost $19.5 million, have been under construction for several months.
About 3km of pipes have been laid but contractors have "almost stopped work" while the council seeks independent advice, Queenstown Lakes District Council engineering manager Mark Kunath told the Wanaka Community Board this week.
"We will hold off putting [any more] pipe into the ground until we sort out which joints we want tested," he said.
Welding records showed welding machine settings appeared to have sporadically changed from the English standard to the German standard.
The council specified the English standard.
The council has been looking to find an independent person to review about 450 welds.
Random tests on seven joints had been carried out under both standards by cutting out and destructively testing welds.
To date, they had all come back with satisfactory results.
Mr Kunath said the project continued to meet its budget, and the September deadline was still on track.
Wanaka Community Board chairman Lyal Cocks said when contacted if the work was unacceptable, the pipes that had already been laid would have to be dug up and the welding would have to be redone.
That would be "expensive for someone, but not us", he said.
It could also delay the project.
The contractor is Fulton Hogan.
Project manager John Dunn could not be contacted for comment.
