How Much Water Should I Drink?

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. Sooo… why doesn’t this article end right here?

Because there are a few exceptions. Plus, 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. 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.

When I give workshops, I often go through client case studies — asking the audience to tell me what they would suggest. Without fail, someone raises their hand and proclaims: “The first thing I’d do is have them drink more water.” “Why?” I ask. That’s when they tell me: “Well, most people are dehydrated.” This is a misconception. 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. Most people drink when they’re thirsty, and do just fine — no special formulas or calculations required. 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. Unless, however, you’re an athlete, elderly, or pregnant.

How much water should athletes and exercisers drink?

Though your thirst mechanism works well during rest, it doesn’t function as well during activity. We’ve known this since the 1930s when researchers asked a man and a dog to walk just under 20 miles (32 km) in the 104F (40C) heat of Boulder City, Nevada. Both the man and the dog could drink whenever they wanted. But only the dog finished well hydrated. The man, on the other hand, lost about 6 pounds (3 kg) of his body mass through water loss.

Research shows that, when people doing intense exercise rely on thirst alone, they tend to under consume fluid, replacing only about half of what they lose. People can lose 1-2 percent of their body weight very quickly when they’re exercising intensely in a hot, humid environment. That’s enough to raise heart rate, body temperature, and your perception of effort. For aerobic efforts, like cycling, it’ll also slow you down.

In addition to the liter of fluid you get from food, consume at least 3 liters (101 ounces) of fluid on the days that you exercise. That breaks down as follows:

1 liter (34 ounces) before and during exercise
1 liter (34 ounces) after exercise
1 liter (34 ounces) throughout the day, with roughly 1-2 cups of water with each meal
During long-duration and/or intense exercise, of course, you lose more than just water. This includes sodium, potassium, and other electrolytes — and it’s important to replace those, too. Otherwise you risk hyponatremia (sodium deficiency).

So, instead of plain water, consume an electrolyte beverage (such as a sports drink) for exercise lasting more than an hour in intense heat and/or humidity or more than two hours in any condition.

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

✓ Non-athletes

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. So 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. If you compare your urine color to what’s shown on the chart below, you’ll get an answer that’s almost as accurate as an expensive hydration test that your physician or trainer would run in the office.

This option works best for:

✓ People who live in hot, dry environments and worry about dehydration

✓ People whose jobs make on-demand drinking difficult (such as a healthcare worker who wears a mask for a 12-hour shift)

✓ People who exercise moderately in hot and/or dry environments

✓ People who are pregnant

✓ People age 65 and older

In summary, you’re probably doing just fine. In terms of hydration, with the above exceptions in mind, you can keep going along as normal. Drink when you’re thirsty, and hopefully not from the toilet.

[This article originally appeared at]