As humans, we like our rules – especially when it comes to health. Hey, some of them exist for good reason. Many of us have been living religiously by the "8 x 8" rule: drink 8 oz of water, 8 times per day. But not nearly as many of us have asked where that rule comes from...

And, as it turns out, it's not based on all that much.

Certainly not actual science, at least. “It has no basis in fact,” says Michael Farrell, a professor at Monash University in Australia, who studies how the brain responds to thirst and other sensations. Don't be mistaken, though, that making hydration a priority is very important. But as with so many other things, how much water each person should drink depends entirely on circumstances: that person, their diet, their unique levels of activity, and their environment, just to name some big ones.

Scientists Just Busted The Popular Water Intake Myth

So without this rule, how will we know how much water to drink? It's actually not hard to figure out. First and foremost, your body actually has a thirst sensory system, designed to tell you when you need water. Your brain has thirst neurons, which detect various signs of dehydration and send signals to your throat to get thirsty. Once someone takes that first swig of water, refreshment takes over from head to toe. It feels glorious, doesn't it?

But then, if water needs to reach the stomach, go through the intestines, and be absorbed into the blood stream to actually hydrate the body – taking about 10 minutes in total – why does merely sipping the water seem to do the trick?

Well, it's just that: a trick.

The brain’s hypothalamus, which regulates appetite and other vital functions, works together with the mouth and throat – heightening the distracting sensation of dryness, and communicating the presence of water and incoming hydration. The brain sends out thirst signals, and the mouth and throat send back hydration signals, which the brain rewards with the feeling of "satiation." It's quite amazing – and this way, as long as you pay attention, staying hydrated should come naturally.

Things like hot temperatures and exercise kick up the amount of water any person should consume, since so much of it will remove itself in the form of sweat. On the other hand, colder days without much movement can lead too much water ingestion to be detrimental to some of the body's natural functions.

Scientists Just Busted The Popular Water Intake Myth

Another thing to keep in mind is food consumed. The Health and Medicine Division of the National Academies has also proven that people get about 20% of their water from food, like fruits and vegetables, and drinks. Along with regular water, milk, juice, and other non-alcoholic beverages count towards your fluid intake. But bear in mind, they also come with unnecessary calories that can increase your need for water intake at the same time. Not to mention, they have their own added health risks, such as diabetes and heart attacks – just one of many reasons they shouldn’t be relied upon for hydration. However, if consumed intentionally and consciously, these dietary contributions can really help out with hydration.

Now, senior-aged people are recommended to be a little more precautious with staying hydrated; somewhere between 6% and 30% of people over 65 who are hospitalized are dehydrated. But other than this age group, people generally just need to be aware of their circumstances, such as personal physical activity or extreme climates – and pay attention to the mind and body, which work together to let you know you need water before any of that happens.

Christopher Zimmerman, a grad student in neuroscience at the University of California, San Francisco, reminds us of the most important signs of hydration or lack thereof to watch out for: clear urine is a good sign, while yellow or otherwise dark urine signals dehydration. Rapid breathing, fatigue, fever, and dizziness are all signs more water is needed – along with less common blotchy skin and dry or blue lips.