Every month, tens of thousands of people ask Google:
“How much water should I drink?”
And Google points them to stories that go something like this:
“Most people are dehydrated—and they don’t know it.”
They list headaches, constipation, bad breath, and other dehydration dangers. And they encourage you to guzzle water, lest you dry up like a sad raisin.
In reality, however, the answer to “how much water should I drink?” is incredibly short and simple:
If you’re thirsty, drink something. If you’re not thirsty, don’t worry about it.
I’m guessing you might not believe that staying hydrated is so simple.
So let’s walk through how much water you should drink together.
Why do you need water?
You might’ve already heard:
Your body is more than 60 percent water.
It uses that fluid for some obvious things—blood, sweat, tears—and some less obvious things: regulating body temperature, helping your body make hormones, and stopping your brain from smashing into your skull when you’re doing burpees.
It’s true that chronic dehydration can raise your risk for a host of problems no one wants to have: kidney stones, urinary tract infections, and negative cognitive and physical performance.1
But there’s a difference between chronic dehydration (being mildly dehydrated a lot of the time) and acute dehydration (which is more severe, and requires timely intervention).
Most people are not chronically dehydrated.
According to the Center of Disease Control’s National Health and Nutrition Examination Survey (NHANES), the average US adult easily meets—and even surpasses—their water needs.
Thirst: Actually a pretty reliable sense.
Our sense of thirst works exquisitely.
A part of our brain, called the lamina terminus, monitors blood volume and blood osmolality (the ratio of salt to liquid), among other factors, to determine whether the body needs more or less fluid. If blood volume drops and osmolality rises, the brain turns up that dry feeling in our tongues and throats.
How much water do you need?
Humans need about 3 liters (101 ounces) of fluid per day, though the exact amount will vary from person to person.
Depending on someone’s diet, about 34 ounces (1 liter) of that will probably come from food, especially if they’re eating watery foods like veggies, fruit, prepared oatmeal, or yogurt.
That leaves about 2 liters (67 ounces) to get from beverages.
So the old “drink 8 cups of water a day”—which adds up to 64 ounces—is actually a pretty good general rule.
How much water you need will depend on a range of factors, like age, weight, health status, and activity level, to name a few. If you’re small and sedentary, you might need less than 3 liters. If you’re in a larger body and also exercise in a hot humid environment, you’ll need more.
That’s why thirst is probably a much better gauge than forcing yourself to guzzle a predetermined volume.
How to calculate your water needs
How do you make sure you’re hydrated?
You have two options.
Option #1: Drink when you’re thirsty
This super-simple option works for most people, including:
✓ People who live in cool-to-moderate climates
✓ People younger than 65
Option #2: Monitor your urine
Some people occasionally suffer from acute dehydration.
Like when lots of stuff is coming out of both ends due to food poisoning or an infection. Or when exercising intensely in a hot climate.
As long as they replace what they lost, it’s no big deal.
How do you know if you’ve replaced what you’ve lost?
The answer: Check your toilet.
The more dehydrated you are, the greater your urine osmolality (saltiness).
Luckily, you can also assess osmolality through color: The greater the osmolality, the darker your urine.