How much water should you be drinking? How important is hydration, really? Short version: it’s really fucking important. The science is pretty clear on the benefits of water and the dangers of dehydration.
That’s because water does an overwhelming number of beneficial and non-optional things in your body— without optimal amounts of water, you perform worse on cognition tests, can’t lift as much, and get fatigued more easily. Without any water, you die.
Hydration is critical for athletic performance, for cognition, for gastrointestinal function, for kidney function, the list goes on. Some doctors go so far as to call water an ‘essential nutrient’, alongside carbs, proteins fats, vitamins, and minerals
But, it’s much less clear on exactly how much water you should be consuming each day—because there are so many factors involved.
You have to take into account environment (you need more water when it’s hot), activity level (you need more water when you’re exercising), and diet (if you’re consuming a lot of diuretics like alcohol and caffeine, you need more water). You’re also already consuming some water anyway: most foods also have some water content, and beverages like soda and coffee have even more.
Then, there’s electrolytes. The water in your cells contains a decent amount of trace water-soluble minerals (sodium, potassium, magnesium, and others) that your body needs to function. Drinking a ton of water without the corresponding minerals leads to poor absorption of that water, meaning that you’ll have to drink more and more frequently to stay adequately hydrated.
Similarly, your body stores carbs in your liver and muscles in the form of glycogen, which is basically a bunch of glucose molecules bound to a central protein—and to three or four grams of water. If you’re eating a low carb diet, you don’t retain those carbs and as a result, don’t retain that water; again meaning that you have to drink more and m4ore frequently.
So: how much water?
I like to think about water intake the same way that I think about other nutrients: as a ratio based on daily calorie expenditure. Recent research backs me up on this, and provides some specific numbers to shoot for. Namely, around 1 mL/calorie, or two liters of water per day for someone who needs 2000 calories per day.
If you want to get deep into it, go here and calculate your total daily calories needed—that’s your total water needed (in mL). But for the lazy, the rule of thumb “.5 to 1 oz per lb bodyweight” is close enough—meaning that a 150 lb person would want to drink something like 2.25 to 4.5L per day.
Within reason, more than that won’t do much harm. Less definitely will. So feel free to drink more than that upper bound if you’re still thirsty, it’s hot or dry out, and when you’re exercising. People with healthy kidneys can drink something like 12L of water in a day without issues beyond having to find a toilet every 30 minutes.
It’s prudent to spread your drinking out throughout the day just so you don’t run into a situation where you’re slamming two liters of the cold stuff right before bed, but it otherwise doesn’t really matter when within a 24 hour period your get your water, especially if you’re eating some carbs and/or if you add electrolytes to the mix. There are special tablets and liquids you can use for this purpose; a pinch of low sodium salt works almost as well — specifically low-sodium salt because it replaces some of that sodium with other electrolytes like potassium and magnesium.
My most practical recommendation is just to get a non-disposable bottle like a Nalgene (I use this one) or Hydroflask (Coleman uses this one) and keep it on your desk at work. Every time you notice it, take a couple of sips. Fill it up at every meal, and before every workout. No need to overthink it or measure everything perfectly.