How Much Water Should I Drink Daily?

"Drink 8 glasses of water a day."

You've heard it from your mom, your fitness tracker, and your coworker who swears aloe water helped her skin, digestion, and possibly her student loans. But is this "8 glasses" rule backed by science? Or just one of those wellness clichés that won't die? Let's look at the facts.

Who came up with the "8 glasses a day" rule?

The idea likely traces back to a 1945 recommendation by the U.S. Food and Nutrition Board, which stated that adults should consume about 2.5 liters (roughly 84 ounces) of water per day. However, what is often overlooked is that they also mentioned that "most of this water is contained in prepared food."

Somewhere along the way, that context got lost, and we were left with a blanket "eight 8-ounce glasses" rule. Does that simple rule hold true for all of us?

So, how much water do you actually need?

The fact is, hydration needs are personal. They vary based on your height/weight, activity level, environment, and where you are. For instance, if you're out sweating in the sun, you’ll need more water than if you’re binge-watching TV in an air-conditioned apartment.

According to the National Academies of Sciences, Engineering, and Medicine, the average daily water intake recommendation is:

• About 3.7 liters (125 ounces) for men
• About 2.7 liters (91 ounces) for women

That includes all fluids such as water, tea, juice, and yes, even that third cup of coffee. Water-rich foods like cucumbers, watermelon, and soups also count.

What happens if you don't drink enough water?

Mild dehydration can make you feel tired, dizzy, unfocused, and cranky. Chronic dehydration can even affect kidney function, skin health, and, if you're an athlete, your performance.

How do you know you're dehydrated? If your body had a red flag system, your pee is it. You might be dehydrated if your urine is dark yellow, amber, or brown. Your body is conserving water, resulting in more concentrated urine. Clear or pale yellow urine means you are well-hydrated.

How much is too much water?

Surprised to know that's a thing? It's called hyponatremia, and it happens when you drink too much water. What happens is that your kidneys can't get rid of all the excess water, which dilutes the sodium in your blood. It's rare but serious and more likely in endurance athletes who chug water without replenishing electrolytes.

As with most things in life, balance is key.

How to tell how much water you need

Instead of counting glasses, try this:

• Check your thirst: Pretty basic!
• Look at your urine color: Not glamorous, but effective.
• Consider your lifestyle: If you're working out, spending time in the heat, or breastfeeding, you'll need more.
• Use a calculator: The University of Florida offers a hydration calculator that considers weight, activity level, the climate you live in, and more.

Hydration basics

The "8 glasses" rule isn't usually harmful, it's just not universally correct. It's a decent starting point, but your body deserves more nuance than a vintage rule-of-thumb from the '40s. So listen to your body and drink water when you're thirsty. And if you're still unsure? Just check your pee.

Staying hydrated doesn't have to be complicated or boring. Reach for a can of mainelove sparkling water made with crisp, clean Sebago Lake water and zero sugar. Available in three refreshing flavors, it's an easy (and delicious) way to keep the hydration habit going.

Image: Zack Bowen/Maine Studio Works