My friend Kate has become very basic lately. She seems to have a bottle of alkaline water with her at all times and, the way she goes on about it, you’d think it was the elixir of life. It has improved her skin! Upped her focus! Tastes great! Someone bought her a bottle of the stuff when she was hungover (it’s brilliant for hangovers!) and she’s been a convert ever since.

She’s not the only one. Alkaline water, which is water that has been treated to have a higher pH level than the 6.5-7.5 pH range of most tap and bottled water, is experiencing a surge of popularity. Beyoncé helped kickstart the trend in 2013 when reports surfaced that she included alkaline water on a rider for her Mrs Carter Show world tour. Tom Brady is another celebrity who has professed his love for the stuff. According to data from the Beverage Marketing Corporation, a research and consultancy group, the alkaline water market has grown from being a $47m business in 2014 to a $427m business in 2017. It’s projected to be worth $687m by the end of 2018.

There are a variety of alkaline water brands on the market including Core, Essentia, and Alkaline88. Essentia has a pH of 9.5, achieved after putting regular water through an ionizing process that removes acidic components. This, the company claims, results in “better hydration”. Alkaline88 meanwhile, has a pH of 8.8 “designed to obtain optimum body balance”.

Why would drinking water with a higher pH level be better for you? Dr Tanis Fenton, an adjunct professor at the University of Calgary and an evidence analyst for Dietitians of Canada, told me that the marketing claims behind alkaline water are based on an old idea called the acid-ash hypothesis. This posits that eating certain food like meat, dairy and eggs results in something called acid ash in your body, which increases your acid levels and causes adverse health effects including osteoporosis.

In 2002 an alternative medicine practitioner called Robert O Young spun the acid-ash hypothesis into a fad alkaline diet, with a popular series of books called the pH Miracle. According to these books, an alkaline diet could treat all manner of woes, from poor digestion to cancer. Young, by the way, was sentenced to three years in jail in 2017 for practicing medicine without a license.

While people have been touting the benefits of upping your alkaline levels for decades, Fenton says the belief is not supported by any scientific evidence. Fenton, who analyzed studies looking at the association of alkaline water with cancer treatment, notes that while “there are a few very poorly designed studies” that suggest alkaline water confers health benefits, there is no rigorous evidence this is the case.

What’s more, Fenton stresses, you simply can’t change the pH of your body by drinking alkaline water. “Your body regulates its [blood] pH in a very narrow range because all our enzymes are designed to work at pH 7.4. If our pH varied too much we wouldn’t survive.”

While you can’t change the pH of your blood, your diet does affect the pH of your urine. “Most people’s urine is about 6, which is acidic,” she explains. However, “that’s no problem, that shows our kidneys is working.” So while it’s possible drinking alkaline water may make your urine less acidic, that doesn’t really make a difference; you’re literally just flushing money down the drain. Ultimately, says Fenton, alkaline water is a solution to a problem that doesn’t need solving.

If alkaline water is junk science why is it so popular? “It sounds plausible,” says Tim Caulfield, the author of Is Gwyneth Paltrow Wrong About Everything?, which debunks celebrity health advice. “It is a science-y sounding idea that has intuitive appeal. Alkaline water is also part of the multitrillion-dollar wellness industry, much of which is built on the marketing of science-free products and practices. There seems [to be] an unquenchable thirst for new and unique strategies for maximizing health and avoiding disease.”

As well as riding the wellness wave, alkaline water is also part of a “rising connoisseurship around water”, says Lucie Greene, the worldwide director of a trends and consumer behavior group at advertising agency J Walter Thompson. Bottled water recently became the number one drink in the US for the first time in history, overtaking soda, which is declining in popularity.

“We’re seeing multiple trends and selling points within water at the moment,” Greene explained over email. “From ‘raw’ water (literally water from the ground) which was popularized by Silicon Valley Burning Man advocates, to water with electrolytes. There are now halal mineral waters. And waters that have been doctored to have special properties and benefits, like Oxigen, the oxygenated water brand that claims to boost the benefits of water by harnessing O4, a proprietary molecule that delivers a concentrated dose of oxygen.”

Greene also notes that Instagram has radically “accelerated the pace of food, drink and health trends”. We’re seeing things move “from fringe to global trend at a much faster rate than before”. Brands including Essentia have capitalized on this with influencer marketing and paid social media placements.

If alkaline water is just a fad with no scientific basis, however, what about people like my friend Kate, who swear they feel its benefits?

Well, says Dr Fenton, it’s possible that they’re drinking more water than they were before, which is not a bad thing. Also, she says, “have you heard of the placebo effect?”