Experts are cautioning Kiwis against diving into the world's latest natural health craze - untreated, unfiltered "raw" water.

In some parts of the US, there's been a drive in alternative health circles to "get off the water grid" and drink spring water that hadn't been filtered, treated, or even sterilised.

One San Francisco grocery store was selling 9 litre orbs of the water - claimed to have "a vaguely mild sweetness, a nice smooth mouth feel, nothing that overwhelms the flavour profile" - for NZ$50 each.

There didn't yet appear to be any companies following suit here, but scientists have warned Kiwis not to try sourcing their own - and stick to their town supply.

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"Consuming untreated water is like driving your car without wearing a safety belt - you might get away with it, but you are taking an unnecessary risk," said Michael Baker, a professor of public health at Otago University in Wellington.

New Zealand surface water was heavily contaminated with microbes that could cause sickness - among them protozoa such as giardia and cryptosporidia, or bacteria like salmonella and campylobacter, which struck down more than 5000 Havelock North residents in 2016.

There were also increasing cases of serious, and occasionally fatal, shiga-toxin producing E. coli infections, Bakers said.

"From a health and sustainability perspective, the science supports use of treated, fluoridated, reticulated water supplies as the main source of drinking water in most situations.

"There are of course exceptional circumstances where people need to use alternatives, such as boiled water if local water treatment is inadequate – which may for example occur when water treatment systems are overwhelmed by heavy rainfall events."

Baker dismissed claims by producers of raw water being superior to properly treated water as "idiotic".

"Effective treatment of drinking water is one of the most important public health measures in history - so successful that many of us now take it for granted," he said.

"Perhaps that is why some consumers are attracted to the idea that water treatment is optional."

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University of Waikato biological sciences lecturer Dr Alison Campbell, who was moved to write a blog post on the issue, also said there was no validity in claims that bacteria in raw water acted as probiotics.

"Raw water isn't going to be magically better at hydrating people, to address just one of the claims made for it in the US."

Water treatment used chlorination, ozone, or UV treatment to provide safe drinking water - since raw water contained none of that, consumers were at risk of potential contamination, Campbell said.

Society for Science Based Healthcare chair Mark Hanna slammed the products as "quackery", saying it smacked of a "water purity concept that goes hand in hand with anti-fluoridationism".

"Which is rather ironic considering their primary selling point is all the things in there that aren't water," he added.

"Of course, if anyone's really concerned about getting probiotics there are better places to get bacteria than by drinking untreated water - ones that won't get you sick too.

"I really hope no one starts bottling unswimmable New Zealand river water and selling it as 'raw water'."

In any case, Baker said, selling untreated drinking water here was illegal - bottled water was covered by the Food Act and there were also stringent industry standards for such products.

"If consumers are concerned about the taste of their tap water they can install domestic water filters to safely remove chlorine immediately prior to drinking," Baker said.

"Resorting to bottled water is generally unnecessary, expensive, and produces large amounts of plastic waste."