"We've ruled out a number of potential causes including cross-contamination, backflow, rust in pipes and silt from source water," it said in a statement published on its website.
"Having ruled out all of the above, we believe the most likely cause of the discolouration is non-toxic microscopic algae in the raw water which is common in summer, and is killed by our water treatments. This reaction can discolour the water."
Maybe the council should call in Aroha to fix things up?