Why that 8-by-8 rule isn’t true.

There’s really no good advice for water intake.

When people ask me for one small, easy thing they can do to improve their health, my first answer is almost always, “Drink more water.” It sounds like canned advice, but many people can stand to drink more water, and it can be a quick fix to common ailments like minor headaches and fatigue that aren’t explained by other conditions.

Water isn’t a cure-all, but it is a necessity. If you don’t drink water (or water in the form of some other fluid), you will die. It’s that simple, and water is that important.

It’s tough to know how much water you really need when there’s so much different advice out there. In this article, learn the true recommended intake for water, plus several factors that influence your hydration needs.

Read more: The best water bottles to buy in 2020

How much water to drink 

It’s usually not a bad idea to sip on some water.

You’ve heard the adage — we all have. Drink eight glasses of water at 8 ounces each. It’s the eight-by-eight rule that guides us to drink 64 ounces of water each day. Many of us have blindly followed this advice for our entire lives, not knowing where it came from or why we need eight glasses of water.

Apparently, the eight-by-eight rule appeared out of a void, because there’s no scientific evidence to back it up. It’s just another one of those long-standing myths that people believe because, well, that’s what everyone believes. While drinking 64 ounces of water each day isn’t a bad thing, it could be too much or not enough for some people. 

Other guidelines exist, but there’s still no true consensus. There’s no formal recommendation for how much water people should drink every day, perhaps because everyone needs different amounts of water. 

There is, however, an “adequate intake” of water for adult men and women. This adequate intake includes water from non-water beverages, such as milk, sports drinks, tea and yes, even coffee. It also includes water from fruits, vegetables and other foods (think of how much water goes into a bowl of oats or soup!). 

The adequate intake (p. 73) is 15.5 cups (3.7 liters or 125 ounces) for men and 11.5 cups (2.7 liters or 91 ounces) for women. However you choose to consume these 125 or 91 ounces of fluid is up to you. And, though this is the closest thing we have to a recommended daily intake, even these numbers vary from person to person depending on a number of factors.

You might need more water if… 

When you lose fluids through sweating, replace them with water or sports drinks.

You have an active job: Those on the go all day (especially those who work outdoors) may need more water than most people. The more you move, the more you sweat, and you should replace lost water through fluid intake. 

You exercise often: If you don’t have an active job but you do exercise a lot — whether in the gym or through recreational activities — you also need more water than most. Even if you don’t realize it, you lose a lot of fluids during physical activity (even in cold weather). Up your water intake to account for activity.

You live in a hot climate: Hot weather means increased sweating, and it’s important to replace lost fluid. Dryness compounds fluid loss in hot weather — people in desert climates may need more water than those in tropical climates.

You’re pregnant or breastfeeding: Pregnant people need more water to encourage improved circulation, increased calorie intake, and other physiological processes to support the growth of their baby. Breastfeeding people need extra water to support breast milk production.

Various rules of thumb for hydrating

Keeping a glass of water at your workstation can help you drink more water.

Different people follow different rules for hydrating. These four common guidelines can help you stay hydrated no matter what kind of lifestyle you have.

Drink when you’re thirsty: There’s some controversy surrounding this method. Some health professionals say you shouldn’t overcomplicate hydration and your body tells you when it needs water. Others say waiting until you’re thirsty is waiting too long — that you’re already dehydrated when you feel thirst. Some people seem to have stronger thirst mechanisms than others, so this method may or may not work for you. 

Drink a glass before meals and between meals: This isn’t bad advice. Structuring water intake around a ritual like mealtime can ingrain hydration as a habit. However, your total water intake will vary depending on how many meals you eat. If you eat three meals, you’ll drink five glasses of water according to this rule, which may not be enough (unless they’re big glasses). If you don’t have a routine eating pattern, this rule probably won’t work for you.

Drink eight glasses a day: Again, one-size-fits-all health advice rarely works for all people. If you feel adequately hydrated on 64 ounces of water each day, that’s great. If you feel overly hydrated (clear pee and very frequent urination), cut back slightly. If you feel dehydrated (dark pee, headaches, infrequent urination), eight glasses may not be enough for you. 

Drink half your bodyweight in ounces: This is a simple guideline that’s easy to remember and usually easy to achieve. If you weigh 150 pounds, aim to drink 75 ounces of water each day. This is the only rule of thumb that accounts for different body sizes, but it doesn’t account for thirst, climate, activity level or other factors. 

Experiment with hydration techniques to find what works for you. As long as you’re not battling chronic fatigue, headaches or other signs of dehydration, you are probably doing a pretty good job.

The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health provider regarding any questions you may have about a medical condition or health objectives.