Hundreds of companies are getting away with dumping contaminated waste into public sewers, potentially damaging the infrastructure and the environment.
Data from 68 councils shows some of the biggest companies have repeatedly breached their trade waste consents over the last year.
But none have been prosecuted, and due to a legislative error they can't be fined either.
RNZ can reveal successive governments have known about the issue for nearly two decades.
Here's investigative journalist Anusha Bradley with the story.
