A lot of people have got a lot of money riding on the belief that humans must drink 8 glasses (2.5 litres) of water each day.
At the front of the queue? Bottled water companies who've made billions selling us the same stuff we can get out of our taps for free.
They're closely followed by isotonic sports drink makers who insist that those 30 minutes spent on the treadmill will result in the loss of potentially fatal amounts of electrolytes unless we promptly rehydrate with a bright blue sugar-laden drink.
Let's not forget the more recent trend of plant waters.
Those driving the trend want us all to replace good old H2O with extortionately priced fluids tapped from virgin coconuts, birch trees and even cacti.
This, perhaps, explains why the myth that we all have to drink a specific quantity of water each day continues to persist, even though it has been disproven time and time again.
So, let's put this issue to rest once and for all.
An impressive 2002 paper published in the American Journal of Physiology smashes the myth to pieces - it's worth a read if you have 10 minutes to spare. In short, the paper's author Heinz Valtin pinpoints the following statement made by the Food and Nutrition Board of the National Research Council in 1945 as the origin of the myth:
A suitable allowance of water for adults is 2.5 litres daily in most instances. An ordinary standard for diverse persons is 1 millilitre for each calorie of food. Most of this quantity is contained in prepared foods.
But it seems the last sentence, which clearly states that the bulk of the water an adult needs is found in the food we eat, was ignored. This, in turn, led to the idea that the average person needs to drink 2.5 litres of water daily.
So back to the question at the heart of this blog: can a person stay properly hydrated without drinking water?
The answer is a resounding yes.
There's water in so much of the food we eat that we don't need to drink the stuff to remain hydrated. Fruit and vegetables, like cucumber and berries are up to 90 percent water. And contrary to popular belief, 'bad' drinks like coffee, alcohol and even fizzy drinks all count towards your daily fluid intake because they too contain a lot of water.
But as someone who makes her living from writing about health and fitness, and advising others on how to optimise their health, it's safe to say that I don't think swapping water for double espressos and coca cola is a great idea.
So what's my point then?
It's the same one I regularly make: don't believe the hype.
There's no specific amount of water you need to drink each day. The amount you need will vary from day to day depending on the temperature, how much sweat you've lost, the food you've eaten, etc.
Let your thirst levels guide you. And if you're a little out of sync with your thirst cues, use the colour of your urine as a reminder - if it's darker than a light straw colour, it's time for a drink.
For those who consider eating healthily a priority, it goes without saying that drinking plain water is the quickest way to rehydrate. But while I've always struggled to understand people who say they don't like the taste of water (which is like saying you don't like the smell of fresh air), I appreciate that drinking water is a legitimate problem for some.
And my heart goes out to you because so many 'healthy' alternatives to water are secretly packed with crap (usually artificial sweeteners and flavourings to mimic exotic fruit flavours), which means you've got to be pretty observant to avoid loading your body up with rubbish when trying to stay hydrated.
My advice? Man up and drink some water - it's not meant to taste delicious.
If you really can't do it, throw in a few slices of fresh fruit to add some flavour.
And if that sounds too much like hard work and you'd rather opt for 'healthy' flavoured waters, read the ingredients label of all drinks... just to make sure they're as healthy as you think they are. There are some good options on the market that are low-calorie; free of added sugar, sweeteners and preservatives; and actually taste nice.
But there are a lot that, well... aren't.
Here's a little head-to-head to demonstrate my point.
Take the new Swiss drink Purelosophy and the supermarket favourite Juicy Water. Both are marketed as water with a splash of fruit extracts. But take a peek at the ingredients label of both and you'll find that Purelosphy drinks really do contain just alpine water mixed with fruit and herb extracts, while Juicy Water contains spring water, lemon and lime juice, and a load of added sugar - 37g per 250ml bottle to be precise!
The moral of the story? I've said it before, but I'll say it again: don't believe the hype.
The original version of this article appeared here on drlaurettaihonor.com, where you can find realistic strategies for eating better and getting into shape.