“It’s a short term fix to improve the optics. They’re basically dehydrating to increase definition, which can be pretty dangerous,” says Mullan.

That’s not to say water can’t work as a weight loss aid. Fortunately, as the science shows, drinking a few extra glasses of water a day could help you shed those extra pounds.

It doesn’t take a scientist to tell us that water can help fill us up. Downing a glass of water can be incredibly effective, especially if you’re snacking out of boredom, or you’re simply dehydrated.

“Water can help you feel full and act as an appetite suppressant,” confirms Mullan. “If you drink water before a meal your stomach will signal to your brain that it’s full and you’re likely to eat less.”

In one 2014 study, published in Journal of Science Biology and Medicine, 50 overweight women were instructed to drink a half litre of water 30 minutes before breakfast, lunch and dinner, for eight consecutive weeks. They lost an average of 3.5lb and also saw reductions in body fat and BMI.

Staying hydrated can also help nip that snacking habit in the bud.

“Often we think we’re hungry when we’re actually thirsty,” explains the Body Retreat co-founder Juls Abernethy. “I’d suggest drinking a glass of water before you reach for a snack. You’ll often find the moment has passed and you don’t need that biscuit after all.”

Certainly reaching for a glass of water can help curb your overall liquid calorie intake, as research shows. Replacing one sugar sweetened drink a day with water can produce a noticeable weight loss, as one study showed. Women and men who made the substitution gained 1.3lb less in four years, compared with those who did not, and saw greater benefit than those who substituted a low-calorie diet drink, who only gained 13.7oz less than the sugary drink consumers.

Staying hydrated might also help reduce bloating, particularly if your bloat is down to constipation. “You need fluid in your system to keep everything moving,” confirms Abernethy. “When waste builds up in your body, you can soon feel uncomfortable and bloated.”  

Going on a short water fast, of no more than 24 hours (any more could be dangerous without medical supervision), will lead to fast weight loss as the glycogen stores in your liver plummet. That’s largely because glycogen is a water magnet. But this fast weight loss is usually only temporary.  The scales bounce back as soon as you start eating carbs again and your glycogen stores in the liver and muscles fill back up.   

However, there could be other benefits from short water fasts, as some studies have linked them to reduced risk of cancer, by promoting autophagy, the body’s way of clearing out damaged cells and heart disease.

Staying hydrated helps us exercise more efficiently. “Water is needed for countless processes in the body,” explains Mullan. “When you’re dehydrated, your blood becomes thicker. The heart has to pump harder, especially in cardiovascular exercise. It’s certainly worth remembering to drink before, during and after exercise to avoid dehydration.”

Staying hydrated might also improve our ability to burn fat, say scientists. That’s because the first step of the fat metabolism involves water, when water molecules interact with triglycerides (fats) to create glycerol and fatty acids. If we’re dehydrated this chemical process could be impacted.

A 2016 review of animal studies found that when animals were fully hydrated, not only did they tend to eat less, they also saw increased lyposis (fat burning) and fat loss.

There’s no recommended standard for water intake – though many of us don’t drink enough.

“The amount you need depends on different factors, like body weight and how much you exercise and how hot it is,” says Abernethy.

The National Academy of Medicine in the US suggests nine cups of water for the average woman, and 13 cups for men (with one cup equalling 8oz), while the NHS Eatwell guide says we should drink six to eight cups of fluid a day.

As with anything, it’s possible to have too much of a good thing.

“If you drink too much water, it’s pretty dangerous,” confirms Mullan. “In hospitals if you give too much fluid, sodium tends to dilute, which can lead to swelling of the brain. That’s what we saw in many of those kids who died after taking an ecstasy pill, when they’d drunk loads of water.”

So water loading is out. As with so many things, little and often is best.

How to get enough water

• Drink a large glass of water before each meal
• Eat more liquid-rich meals, like soups and smoothies, or load up on juicy fruits and salads
• Make sure you have a glass of water by the bed at night
• Drink before, during and after exercise – more if it’s hot or humid