How Much Water Should You Drink a Day? The Real Answer (and the 8 Glasses Myth)

Eight glasses a day. Almost everyone has heard it, and almost nobody knows where it came from. It isn't wrong, exactly. It just isn't the whole picture, and for some people it's not even close.

The truth about hydration is simpler and more forgiving than the water-bottle influencers make it sound. You don't need to carry a gallon jug around or set alarms for every sip. Let's go through what the experts actually recommend, what counts toward your total, how to tell if you're getting enough and when you really do need more.

How much water should you drink a day?

The National Academies of Sciences, Engineering, and Medicine set general intake levels for water in 2004. For healthy adults, the adequate daily intake is about:

Men: 3.7 liters (roughly 15.5 cups)
Women: 2.7 liters (roughly 11.5 cups)

Before you panic, here's the key detail people miss: that's total water from all sources, including food. Food usually supplies around 20% of it. So the amount you actually drink is closer to:

Men: about 3 liters (around 13 cups) of fluids a day
Women: about 2.2 liters (around 9 cups) of fluids a day

And "fluids" doesn't just mean plain water. Milk, tea, coffee, soup and sparkling water all count.

These numbers are averages for healthy people in mild climates. They're a guide, not a quota you have to hit to the drop.

Where did the 8 glasses of water a day rule come from?

Nobody's completely sure. The most-cited origin is a 1945 recommendation from the US Food and Nutrition Board, which said adults needed about 2.5 liters of water a day. The very next sentence, which almost everyone forgot, said most of that amount is already contained in prepared foods.

Over the decades, "2.5 liters, much of it from food" got simplified into "drink eight 8-ounce glasses." It's an easy rule to remember, and it's in the right ballpark for many people. But there's no strong evidence that you need eight glasses of plain water on top of everything else you eat and drink.

Does coffee count toward your water intake?

Yes. This myth refuses to die, but it's been tested. Caffeine has a mild diuretic effect, meaning it makes you pee a bit more, but the water in the cup more than makes up for it in regular coffee drinkers. A 2014 study that compared moderate coffee drinking with the same amount of water found no meaningful difference in hydration. For more on coffee's real downside (your sleep), see caffeine and sleep.

Alcohol is different. It does increase fluid loss, so beer and wine shouldn't count toward your total, and a glass of water between drinks is a good habit.

Foods with the highest water content

You can genuinely eat a chunk of your water. These foods are all around 90% water or more:

Cucumber
Lettuce and leafy greens
Celery
Tomatoes
Zucchini
Watermelon
Strawberries
Cantaloupe
Peaches and oranges
Plain yogurt (around 85%)
Broth-based soups

A big salad, a bowl of soup and a couple of pieces of fruit can add up to several cups of water without a single glass.

When do you need more water?

Your needs go up when:

It's hot or humid, or you're at high altitude
You're exercising or working hard physically
You have a fever, vomiting or diarrhea
You're pregnant (the National Academies suggest about 3 liters of total water a day) or breastfeeding (about 3.8 liters)
You're on a high-fiber or high-protein diet, which both need extra fluid. That's worth knowing if you're fibermaxxing.

Older adults deserve a special mention. The sense of thirst tends to weaken with age, and some medicines (like diuretics for blood pressure) increase fluid loss. Waiting until you feel thirsty can leave you short, so regular drinks with meals and between them are a smart habit.

How much water should you drink when exercising?

For most everyday workouts under an hour, drinking water when you're thirsty and having a glass or two afterwards is plenty. For longer or hotter sessions, a simple approach is to drink before you start, sip during and rehydrate afterwards.

One practical trick athletes use: weigh yourself before and after a long workout. Each pound lost is roughly 2 to 3 cups of fluid to replace over the next few hours.

Do you need electrolyte drinks?

Electrolyte powders and drinks are hugely popular right now, and they're marketed as if everyone needs them every day. Most people don't.

Electrolytes (sodium, potassium, magnesium) help your body hold on to fluid. You lose them in sweat, and you get them back from food. For a typical day at a desk with a walk or gym session, water and normal meals cover it.

Electrolyte drinks can help when:

You're exercising hard for more than an hour, especially in the heat
You're a heavy, salty sweater (white salt marks on your clothes are a clue)
You're recovering from vomiting or diarrhea (an oral rehydration solution is best here)
You're doing physical work outdoors in hot weather

Watch the labels. Some sports drinks are loaded with sugar, and some electrolyte powders contain a lot of sodium, which isn't ideal if you're watching your blood pressure.

How to tell if you're drinking enough water

You don't need to count every sip. For most healthy people, two checks work beautifully:

You rarely feel thirsty.
Your urine is pale yellow, like lemonade. Dark yellow or amber usually means drink more. Completely clear all day can mean you're drinking more than you need.

Some vitamins (especially B vitamins), foods like beets and some medicines change urine color, so don't read too much into one bathroom visit.

Signs of dehydration

Mild dehydration can show up as:

Thirst and a dry mouth
Darker urine, and less of it
Headache
Tiredness or trouble concentrating
Dizziness when you stand up
Constipation

Severe dehydration is a medical emergency. Confusion, a racing heart, fainting, very low blood pressure or no urine for many hours need urgent care. In babies and young children, watch for no wet diapers for three hours or more, no tears when crying and a sunken soft spot on the head.

Easy ways to drink more water every day

Keep a bottle where you can see it. On your desk, in the car, by the couch. Out of sight really is out of mind.
Pair water with habits you already have. A glass when you wake up, one with each meal, one when you get home from work.
Eat your water. Add fruit to breakfast and a salad or soup to lunch.
Flavor it. A slice of lemon, cucumber, mint or a few berries makes plain water more interesting. Herbal tea, hot or iced, counts too.
Try sparkling water. It hydrates just like still water.
Use a straw. Many people find they drink more this way. (A reusable one is kinder to the planet.)
Watch the sugar. Juice and soda hydrate you, but the sugar adds up fast. Water, sparkling water, milk and unsweetened tea are better everyday choices.

Can you drink too much water?

It's rare, but yes. Drinking huge amounts of water in a short time, often during long endurance events or drinking challenges, can dilute the sodium in your blood. This is called hyponatremia, and it can cause nausea, headache, confusion, seizures and in extreme cases death. Healthy kidneys can only clear about 0.8 to 1 liter of water an hour.

If you have heart failure, kidney disease or liver disease, your doctor may want you to limit fluids. Follow their advice over any general guideline, including this one.

Frequently asked questions about drinking water

Does drinking water help you lose weight?

It can help a little. Drinking water instead of sugary drinks cuts calories, and a glass of water before meals may help some people feel fuller. It's a helpful habit, not a weight-loss method on its own.

Is it bad to drink water right before bed?

It won't hurt you, but it may wake you up for the bathroom. Try to front-load your drinking earlier in the day and taper off in the last hour or two before bed.

Is tap water or bottled water better?

In most of the US, tap water is safe, regulated and far cheaper. If you're concerned about your local supply, check your water utility's annual quality report or use a certified filter. It's also kinder to your wallet and the planet than bottled water.

Does tea dehydrate you?

No. Like coffee, tea counts toward your fluid intake for regular drinkers.

Hydration covered? Take the free wellness wheel quiz to see which of your 8 dimensions could use a refill next.