Environment Minister Nick Smith has warned against jumping to conclusions about the cause of the Havelock North outbreak despite fingers already being pointed at local farmers.
Questions have been asked about the culpability of cattle and chicken farmers, as well as a nearby mushroom farm, but Dr Smith says sometimes even the most basic failures could be to blame.
The campylobacter outbreak in Havelock North struck down 5100 people with gastro, closed schools and businesses and has left residents still boiling their drinking water weeks later.
It is a reminder of the E. coli contamination in Nelson where upstream farmers, birds and waterfowl were blamed before testing confirmed the true cause, Dr Smith says.
"It was embarrassingly found that most of the problem was toilets from the council's library having been wrongly plumbed into the stormwater rather than the sewerage system," he told crowds at a Lincoln University environment lecture in Christchurch on Tuesday night.
He said the lesson was to be cautious of jumping to conclusions too soon.
Water contamination was just one part of Dr Smith's presentation, which also addressed concerns about measuring water quality, limits on water takes and proposed strengthening of swimming requirements.
Dr Smith warned a goal of making all waterways swimmable, rather than wadeable, were "unworkable" and "impossible" without a massive bird cull.
But the Green Party has criticised that view as baseless.
"He knows, as we al do, that the real and lasting damage to our rivers is from stock in waterways, farm run-off, sewage and intensified dairy farms among others - he just won't admit it," Green Party water spokeswoman Catherine Delahunty said.
Instead she said her party wanted to see practical solutions for stopping pollution and protecting rivers.
Dr Smith also touched on the need for a stronger national direction for improving freshwater management and a more collaborative approach.
New Zealand had a habit of turning environmental issues into a battle ground with winners and losers where farmers are seen as environmental vandals and environmentalists as economic imbeciles, Dr Smith said.
"I have been trying to lead a culture change at both a national and local level where different water users and interest groups work together on finding solutions that will work for the environment and the economy," he said.