Federated Farmers is urging the public to apply some "good old-fashioned common sense" and scrutinise the statements of "activists" as they push their "anti-farming agendas" in the wake of the Havelock North water-borne gastrointestinal disease outbreak.

Top of federation president William Rolleston's list was Dr Mike Joy's statement on 'The Nation that central and local government had allowed massive intensification (of dairying) that had caused the problem' when in fact the closest dairy farm the federation could find was some 40 kilometres away. And his statement that animals had to come out of agriculture.

"The sanity of this statement for New Zealand can stand on its own merits," Dr Rolleston said.

"In the context of this bacterial episode, he said that 'over time you find it deeper and deeper and deeper (in the groundwater)', when it is known that as water penetrates the ground bacteria are progressively filtered out and their survival diminishes."

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Greenpeace had "waded in with a rant about the Ruataniwha dam and the evils of water storage, but didn't mention that Timaru derives a significant percentage of its town water supply from the successful Opuha Dam", he said.

Others had used the episode to have a go at Overseer, claiming councils were relying on it to manage bacterial risk, when the computer programme modelled the flow of nutrients in the root zone of soil, not bacterial flow into underground aquifers.

Photographs in the media last week of beef cattle standing in the Tukituki River failed to mention that the site was downstream from the Havelock North bores.

"Unless the theory of gravity has changed this is unlikely to be the source," Dr Rolleston said.

"It is worth noting that Waipukurau's treated sewage water outflow is in the catchment above the bores, but this somehow doesn't fit the activist agenda.

"There is no question that animals and birds, both wild and on-farm, create an opportunity for pathogens in the environment. So do humans for that matter.

"Councils have a responsibility to assess and mitigate credible risks which exist in the environment when it comes to drinking water.

There has been a systems failure, and 4000 people got sick. The only way to re-establish confidence in the Havelock North water supply is with good factual, science-based evidence gathering.

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That's what the councils, the Ministry of Health and the local community are trying to do. Distracting rants about building dams, wandering stock and activist theories do nothing to fix the system faster."