Good hydration is essential to keep all of our systems running smoothly. Dehydrated people don’t function as well, cognitively or physically. Drinking water gets linked to everything from weight loss to better skin to healthier joints.
But how much water do you need to survive — and thrive? And is more always better?
Here are some simple guidelines to follow to ensure you’re getting the right amount of fluids in your diet every day.
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How Much Water Should I Drink Every Day?
Humans have evolved to have a strong thirst mechanism for a reason, says Hunter Huston, MD, a nephrologist (kidney specialist) at the UPMC Kidney Clinic at University Center. “It’s the most sensitive trigger for how much fluid to drink,” he says. “Drinking to quench your thirst is a perfectly adequate guide for how much to drink, for most people.”
For people who are otherwise healthy, this means drinking enough water that you don’t generally feel thirsty. If you’re well hydrated, your urine will be light yellow or clear. Dark yellow can be a sign that you’re not drinking enough (though B vitamins can also turn urine bright yellow).
The Institute of Medicine of the National Academies agrees. Their report found that the majority of healthy people drank enough water by following their thirst.
They did set some recommendations for how much water to drink, based on national averages. To recommend how much water a woman should drink a day, they looked at women who were adequately hydrated. These women consumed about 91 ounces of water each day (that’s water from all beverages and foods).
Men who were well hydrated consumed about 125 ounces of water each day, from all sources.
As for the persistent myth of eight glasses of water a day? Not so much, said the panel. That’s a bit of folklore that may have been something a nutritionist named Fredrick Stare wrote in passing in the 1970s.
Dr. Huston says it may have originally come from a series of unofficial Army experiments. Soldiers doing heavy exercise seemed to drink about eight glasses of water, he says.
Drinking Enough Water When You Exercise
For active people, people with certain conditions, and people in hot environments, hydration is even more important.
Some people can lose one to two liters of sweat per hour when exercising, especially in hot weather. “If you’re a heavy sweater and you’re losing 2% to 3% of your body weight while exercising, that’s significant. And you need to replace it,” Dr. Huston says.
What makes hydration during activity a little trickier is that by the time you feel thirsty, you’re already losing fluid. But guzzling a bunch of water all at once in the middle of a workout may cause cramping. “It’s about knowing how much to drink to stay in the range of quenching your thirst and not making you feel gross,” he says.
Athletes need to learn what works best for them. And, he notes, people with kidney disease should always work with their doctor to come up with a hydration plan.
Too Much Water or Not Enough Water Are Both Problems
Dehydration is when you are losing more fluid than you’re taking in. This fluid deficit means that the systems in your body don’t have the fluid they need to work as they should.
Mild dehydration can make you feel dizzy or tired. Extreme dehydration can cause confusion, rapid breathing, and rapid heartbeat. It can be life threatening if severe.
Drinking too much water (like three to four liters) too fast is often called water intoxication, or hyponatremia.
This can cause your sodium levels to drop too low. And the extra water causes your cells to swell, which can be dangerous. In fact, hyponatremia is equally as life threatening as dehydration.
So, we’re back to where we began — with the idea that, for most people, the best approach is to drink to quench your thirst. When exercising, start drinking before you feel the thirst. And stop when you feel replenished.
Editor's Note: This article was originally published on , and was last reviewed on .