A bizarre new trend has emerged in California's Silicon Valley, with people eager to buy large glass containers filled with unfiltered, unsterilised H<sup>20, billed as "raw water" by the company selling it for $36.99 (£27.21) for 2.5 gallons, and $14.99 for a refill.

The trend was discovered in San Francisco by The New York Times and prompted a response from food safety expert Bill Marler.

Marler told Business Insider: "Almost everything conceivable that can make you sick can be found in water."

He warns that because safe drinking water has become the norm, people are unaware of how dangerous natural, unclean and untreated water can be.

"The diseases that killed our great-grandparents were completely forgotten about," he said.

"It's fine until some 10-year-old girl dies a horrible death from cholera in Montecito, California."

Untreated water can lead to the spread of diseases like cholera, E. coli and Hepatitis A, which killed 20 in California during an outbreak last year. Giardia, another illness caused by unclean water, puts roughly 4,600 US people in hospital every year.

"You can't stop consenting adults from being stupid," Marler added. "But, we should at least try."

NYT's story began at Rainbow Grocery in San Francisco, where a store shift manager told them: "It has a vaguely mild sweetness, a nice smooth mouth feel, nothing that overwhelms the flavor profile.

"Bottled water's controversial. We've curtailed our water selection. But this is totally outside that whole realm."

Since the story was published the price of the water, called Live Water, has rocketed up from $36.99 to $60.99.

The Times also spoke with Doug Evans, an entrepreneur whose juicing business collapsed, leading him to discover collecting "raw water" from a local spring, resulting with him and others collecting 50 gallons and selling it on at last summer's Burning Man festival in Nevada.

"I'm extreme about health, I know, but I'm not alone with this," he said. "There are a lot of people doing this with me. You never know who you'll run into at the spring."

The trend stems from unfounded concerns about the treatment of tap water and the effects of chloride, which is entirely safe to drink.