There's no hiding from the Instagram algorithm. Designed to throw out the same kind of content you already spend hours of your life scrolling through, my feed is full of influencers flogging diet tea and dead-eyed YouTubers staring at me from behind the glow of a HiSmile teeth-whitening kit.

Maybe that's why I was recently suggested Alise Miksta's account, which is full of photos of a dream life spent travelling the world, teaching yoga and taking your bra off on mountainsides. However, Alise's account goes one step beyond the usual "wellness" posts about eating raw and practising mindfulness: in the summer of 2019, while she was living in London, Alise started posting about her "no water" regimen, where she replaced fluids with water-rich fruit.

This water abstinence went hand-in-hand with sustained bouts of "dry fasting", where Alise wouldn't eat anything for 24 hours at a time. One of her posts read: "For the first time I did a 24 hour dry fast, (apart from 5 sips of green tea around 11am when it got too cold) and I'm stoked."

Alise isn't alone in her posting about "no water" and dry fasting; she follows a number of accounts run by women promoting the same things, all of them tanned, thin and living transient lifestyles in gap year destinations. For them, this regime doesn't seem to be doing any harm – but experts warn that promoting these dietary choices could potentially be harmful to their followers, of which there are thousands.

Alise is 30 years old, originally from Latvia and currently living in Dubai. Five years ago she went to an ashram in India where a guru told her that carrying around a bottle of water is a "big hype in Europe", adding: "You don't need to do that."

"I believe you don't hydrate from water – water just cleanses," Alise tells me. "So if you eat raw food and fruits, you really don't need water."

Despite saying bottled water is "probably really toxic and dirty", and that official guidance to drink two litres a day is "all business and huge marketing", Alise hasn't sworn off water entirely, estimating she's reduced her intake by 90 percent. But swerving H2O altogether is a point of pride for Sophie Prana, a 35-year-old yoga teacher who claims she hasn't touched the clear stuff in a year.

Sophie is evangelical about "no water", seeking to spread the word through her Instagram account. Her passion for what she's promoting is clear when I speak to her over a crackly WhatsApp line from her current home in Thailand.

"It's the best thing I've ever done in my life," she says. "If you're [eating] a normal Western diet, eating salt and cooked fats, [not drinking water] can be really damaging – but I transitioned into a raw vegan diet, so I hydrate with living water [like melon juice and coconut water] from fruits, and I stopped drinking empty water from bottles or the tap. You hydrate with living water because there's nothing in the water in bottles. It's the water industry that tells us to drink all the time."

While the phrase "living water" might sound a little Goop-y, it has some basis in science. "We know that we don't get our water just from a glass of water – it comes from things like cucumber, watermelon and these really water-rich foods," explains Haleh Moravej, senior lecturer in nutritional sciences at Manchester Metropolitan University.

In certain situations, like after exercise, she continues, the water from plants can replenish minerals our bodies have lost: "Something like cucumber water would be better [than tap water] on electrolytes, because when you do sport you lose salt. Cucumbers will be a better source of potassium and be more beneficial for hydration compared to water [after sport]."

However, as Haleh makes clear, the average person still needs to ingest fluids alongside eating these kinds of foods. "The two main hydrating fluids are milk and water – that's what I know from my years of research and experience," she says. "I would suggest to people: still have your five to ten a day of fruit and vegetables, but also have enough fluid in the form of water or other hydrating fluids."

The notion that you can hydrate by exclusively "eating" water isn't limited to young women on Instagram. Dr Howard Murad – a professor of medicine at UCLA, who describes himself as the "father of modern wellness" – wrote a book called The Water Secret, which claims that eating more water-rich foods is preferable to simply drinking more water.

Dr Murad posits the idea that drinking too much water can flush vitamins and minerals from your body, while the water in food – and the "vitamins, minerals, enzymes, antioxidants [and] phytonutrients" it contains – can be absorbed more slowly and stay in our bodies longer. A study by researchers at the Aberdeen Medical School came to a similar conclusion.

"The point of ingesting water is to maintain cellular hydration – and that's better done by eating your water, which is then released slowly as your food is digested, rather than all at once, which is what happens when you drink your water," Dr Murad tells me. "Unless you're dehydrated as a result of heat or exercise or illness, the water will run right through you."

I ask Elaine Anderson, a freelance dietician with a decade of industry experience, and Haleh Moravej if they're aware of any studies that support the idea of swerving water entirely. They both say no, pointing out that this goes against NHS guidance – and indeed the guidance of the World Health Organisation, Harvard Medical School and just about every health-related website on the internet.

"I would highly discourage people from giving up on water," says Haleh. "Our whole body is 70 percent water... this is a recipe for disaster. Hydration is important for concentration, mood and wellbeing, as well as physical activity. We need water to break down all the nutrients, we need it for our metabolism [...] There's so much more to suggest that dehydration isn't good for you."

Despite the science, or lack thereof, both Sophie and Alise say they haven't run into any problems.

"I stopped eating salt or oils," says Sophie. "I live from watery fruits or vegetables – and this, with dry fasting, is so healthy for your body. People are quite shocked when they hear no drinking or water, but it's a whole science behind it, so when people understand it, it's a whole thing."

The shock Sophie mentions is understandable: after our first conversation, Elaine says that every dietician she speaks to about the subject expresses surprise that anyone would stop drinking water outright. She adds that she's never heard of anyone willingly giving up water for health reasons, telling me humans need it to transport minerals and remove toxins from the body.

This is before we get onto dry fasting, a dietary choice that Sophie, Alise and many other wellness Instagrammers swear by.

Dry fasting means going without food and water for anything from 12 hours to ten days. Various religions use fasting as a way to observe their faith, and have done for centuries, but starving yourself under the guise of wellness is a relatively new trend – and not something professionals see as particularly smart, especially if you're relying solely on water-rich food for hydration.

Various studies have suggested there can be benefits to "intermittent fasting" – where you don't consume any food for around 16 to 24 hours – if you're in good health. However, many of these studies were small, short-term or conducted on animals, and it's been pointed out that intermittent fasting can be dangerous if you're underweight or have a history of eating disorders.

If you plan to fast for over 24 hours, most websites recommend seeking a doctor's advice. Again, studies have found there may be some benefits to prolonged fasting for certain people, but in one study of 768 people fasting for at least 48 hours, 72 percent of participants experienced side effects including fatigue, insomnia and dizziness. The groups advised against this type of fast also extend beyond people with eating disorders to those with Type 1 diabetes or low blood pressure, those taking certain medication, and women who are trying to conceive, pregnant or breastfeeding.

The fact that fasting is being promoted on social media is doubly concerning when you consider the links between Instagram and disordered eating, or the issue of people using "wellness" to mask eating disorders. Compulsively chasing wellness can itself lead to a new condition, "orthorexia", defined by the National Eating Disorders Association as "an unhealthy obsession with otherwise healthy eating".

Elaine has no time for prolonged bouts of dry fasting, describing it as "frightening" and emphasising the lack of scientific evidence behind any supposed health benefits. She says extended periods of fasting can lead to dehydration, hypotension, tiredness and headaches, and also raises concerns about the long-term impact on the kidneys.

Sophie practices "intermittent fasting" between 6PM and 11AM every day, saying that the first time she fasted she "asked the universe for help" and subsequently experienced "extreme healing". Alise undertakes longer periods of fasting, believing food is "a complete distraction and huge attachment". In her words: "I think there is something bigger [in life] than eating breakfast, lunch and dinner, and going to work."

Clearly, living the lifestyle they lead isn't causing Sophie, Alise and others like them too many immediate problems, otherwise they wouldn't be living it. However, actively promoting these dietary choices as a route to "wellness" – with little contextual information or clear safety advice – is where it becomes problematic.

As Elaine points out, "no water" is frequently used as a hashtag on posts about "eating right, clean living and 'wellness'". The danger here is that bundling "not drinking any fluids" in with so many other well-meaning suggestions of self-improvement both opens it up to misinterpretation and exposes the idea to an ever-growing audience of people seeking new ways to be "well".

Unless you're living the kind of extended-gap-year dream life that people like Sophie and Alise have created for themselves, it's hard to access freshly squeezed watermelon juice, or to smash through a kilo of grapes for breakfast. Water-rich fruits and veg can provide hydration – but that doesn’t mean some social media users won't see "no water" and run with a version of the regimen that means simply cutting out water and not replacing any of the lost fluids.

Put simply: a teenage girl in Wigan or Worcester might see one of these shiny Instagram photos and simply stop drinking water, despite living a life that's entirely different to those of the women inside her phone screen.

When I ask both women directly whether they see any dangers in evangelising "no water", neither seems overly concerned. Alise says it's down to each individual user to take what they want from Instagram, telling me: "You have this tool and you make the decision how you want to use it." Sophie is clear that her Instagram shouldn't lead anyone to believe "no water" and dry fasting are overnight cures – and says she tells anyone who contacts her for advice that making such a huge dietary transition needs to be done slowly and with great care.

Dr Murad doesn't seem phased by this prospect either, telling me: "It doesn't concern me much that people will see 'no water' and stop drinking entirely. Their body's sense of thirst will prompt them to drink."

At this point, it hardly needs saying that Instagram can be an incredibly persuasive presence in users' lives, even if the people they're following don't actively intend to persuade them of anything. This is something the team at London's Digital Fairy marketing agency knows a lot about, telling me that Instagram plays an "extremely powerful" role when it comes to wellbeing, as a visual platform that can put pressure on people to look "better".

"Shock health content can create intrigue and engagement, while thriving on the algorithms, regardless of any health benefit," says a representative. "When it comes to health, the conflation of clout with credibility has potentially dangerous applications. You're not risking ending up with an ill-fitting polyester dress from Pretty Little Thing – you could be facing liver damage or heart strain."

And that's the point. Making your own dietary choices is one thing – but preaching about them to an army of Instagram followers who may be ill-equipped to replicate them without the necessary context is irresponsible and potentially dangerous.