It was a sensible move to take fluoridation decisions away from vulnerable councils.

Three weeks ago, when a bug in Havelock North's water supply caused an outbreak of campylobacter, we asked the question, how could this happen in New Zealand? The question was posed not because we imagined New Zealand's water supplies so pristine that E. coli could not enter them, but because we imagined that in a first world economy such as ours, all water supplies would be treated.

Not so. The most surprising discovery for many people, certainly Aucklanders, reading about the contamination of an aquifer in Hawke's Bay, is that not all municipal water supplies in this country are chlorinated. Even a city the size of Christchurch, it seems, considers its artesian water so well protected by the gravels under the Canterbury Plains that it does not take the precaution.

The most urgent question arising from the epidemic in Havelock North is surely not the one still being asked, how did the bug get into the water, but, should we be treating all piped water supplies? This question seems not to be the question in the front of the minds of the Hastings District Council that is responsible for Havelock North. It was not even the first question to be asked of the inquiry set up by the Government. They seem primarily concerned with finding out how the contamination happened, as if such a thing could scarcely be imagined in an aquifer 20m below ground in an agricultural country with a wet climate, porous soils and frequent seismic activity.

The truth is they might never know conclusively how the bug got in. But if they do discover it was attributable to a human error, or to the heavy rain and snow that fell on Hawke's Bay a week or two earlier, would that be a reason not to take the precaution of treating the water supply - all water supplies - from here on?

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The answer seems obvious but, as always where water is concerned, purists will object. Some of our smaller centres, and Christchurch, still dare not fluoridate their water for fear of determined opposition. There will be those who complain they can taste the tiny traces of chlorine that treatment requires and some will say, as did one woman in Havelock North, that it is no good for their hair.

Councils are more vulnerable than governments to impassioned minority views. Councils are elected on lower turnouts and impassioned minorities are more likely to vote than those not concerned at the subject. That is why it was a sensible move by the Government to take fluoridation decisions away from councils and give it to district health boards. If chlorination was to become their decision, tap water would be treated probably everywhere.

The Ministry of Health's "Guidelines for Drinking Water", issued as recently as April, estimated there are 18,000 - 34,000 cases of water-borne gastrointestinal disease in New Zealand every year. Yet when it set drinking water standards for New Zealand in 2005 a number of councils - including Hastings - strongly opposed chlorination and succeeded in ensuring the standards were not mandatory. The Health (Drinking Water) Amendment Act 2007 merely requires water suppliers to "take all practical steps" to comply with the standards.

That act needs to be amended again. The lesson from Havelock North is that treatment should be mandatory. In every town it should be safe to drink the water.