Prosecution was one of ''many tools'' the council could use in response to the pollution, he said.
The previous paint contaminations did not lead to prosecution, because the sources were never identified.
"It can be quite difficult to find the origins of it."
Such pollution was a "real concern" for the council, he said.
"We're also preparing a piece of work on urban water quality. Part of that is raising awareness and making people mindful of what goes down stormwater drains.
"It doesn't just go out of their sight, inevitably it ends up in a river or the harbour."
Kaikorai man Pete Andrews said he saw contractors in the area on Wednesday washing paint into a stormwater drain.
"I came around the corner and I could just see the white paint everywhere."
The contractors were water blasting buckets, brushes and rollers, he said.