How much water should I drink a day? For most healthy adults there is no single magic number. The U.S. National Academies' reference is about 2.7 liters (91 ounces) of total water a day for women and 3.7 liters (125 ounces) for men, counting all drinks and food. Plain water is only part of that.
This is general information, not medical advice. Talk to your doctor or pharmacist about your own situation.
That total includes water, milk, tea, coffee and the water hidden in food. The same expert panel found that most healthy people meet their needs simply by letting thirst be their guide. The numbers below help you picture the target, and the rest of this guide covers when you need more, when you might need less, and the warning signs to watch for.
The National Academies based its reference amounts on what healthy, well-hydrated people actually take in on average. Mayo Clinic gives the same range in cups.
Women: about 2.7 liters (91 ounces, or roughly 11.5 cups) of total water a day.
Men: about 3.7 liters (125 ounces, or roughly 15.5 cups) of total water a day.
From food: about 20 percent of the total usually comes from food. The other 80 percent comes from water and other drinks.
Some rough math: if 80 percent comes from drinks, that is about 2.2 liters (73 ounces) of drinks a day for women and about 3 liters (100 ounces) for men. Treat that as a ballpark, not a quota. The panel said plainly that it does not offer a rule of thumb for how many glasses to drink each day.
The 8 glasses idea is easy to remember. Mayo Clinic calls it a good goal, while noting that some people need less and some need more. In the UK, the NHS suggests 6 to 8 cups or glasses of fluid a day and calls that just a guide. Neither source treats it as a precise rule, and both count drinks other than plain water.
Plain water. It has no calories, so CDC suggests choosing it over sugary drinks.
Milk, tea and coffee. The National Academies panel found that caffeinated drinks can count toward hydration, and that there is no convincing evidence caffeine leads to a lasting shortfall of body water.
Food. Many fruits and vegetables are almost all water. Mayo Clinic lists watermelon, cantaloupe, strawberries, cabbage and squash as examples.
Juice, soda and sports drinks. These count too, but they can add sugar, salt and calories. The NHS suggests keeping fruit juice and smoothies to one small glass (150 ml) a day, with a meal.
Exercise. Sweating uses up water, so drink before, during and after a workout.
Heat, humidity and altitude. Hot or humid weather makes you sweat more, and high altitude can add to fluid loss. The National Academies noted that very active people in hot weather often need six liters or more of total water a day.
Being unwell. Fever, vomiting and diarrhea all cause fluid loss.
Pregnancy and breastfeeding. Both the NHS and Mayo Clinic say you may need more fluids.
Some urinary conditions. Mayo Clinic says bladder infections or urinary tract stones may raise fluid needs. Follow the amount your doctor gives you.
Some people need less fluid, not more. If a doctor has told you to limit fluids, follow that advice rather than any general target, including the numbers in this guide.
You rarely feel thirsty.
Your pee is colorless or pale yellow.
Signs you may be running low include feeling thirsty, dark yellow and strong-smelling pee, a dry mouth, lips and tongue, headaches, dizziness and tiredness. Babies, children and older adults are more at risk of dehydration, so it is worth paying closer attention to how much they drink.
These tips come from CDC:
Carry a reusable water bottle with you.
Freeze water in freezer-safe bottles so you have cold water later in the day.
Serve water with meals, and order it when you eat out.
Add a wedge of lemon or lime for flavor.
Pick water instead of sugary drinks when you can.
It is rare for healthy adults, but it can happen. Drinking far more than your body needs can drop the sodium level in your blood, a condition called hyponatremia, which can be life-threatening. Mayo Clinic notes that some athletes may drink too much before long or intense workouts. More is not always better.
The NHS says to get an urgent appointment or call for medical advice if you have signs of dehydration and:
you feel unusually tired, or your child seems drowsy
you feel dizzy when you stand up and it does not go away
your pee is dark yellow or you are peeing less than normal
you are breathing quickly or have a fast heart rate
Call your local emergency number (911 in the U.S., 999 in the UK) if someone with dehydration symptoms is confused, unusually sleepy or hard to wake, has trouble breathing, has cold skin, or has blue, gray, pale or blotchy skin, lips or tongue.
Yes. The National Academies panel concluded that caffeinated drinks can count toward hydration, and the NHS includes tea and coffee in its daily fluid guide. Watch added sugar, and stick to any caffeine limit your doctor gives you.
There is no official advice to drink a gallon a day. A U.S. gallon is about 3.8 liters, which is more than the average total water intake from all sources the National Academies describes for adults. Very active people in heat can need more. If you are unsure, ask your doctor.
Most healthy people can let thirst guide them. Drink more when you exercise, are in the heat or are unwell, and keep a closer eye on babies, children and older adults, who are more at risk of dehydration.
Colorless or pale yellow is a sign you are drinking enough. Dark yellow, strong-smelling pee can be a sign you need more fluids.
If you want to keep an eye on your own daily goal, Dropkin: Water Reminder is a simple iPhone water tracker. You log a drink in one tap from your saved bottles, glasses or mugs, in ounces or liters, and reminders only arrive during the hours you choose, pause when you are on pace and stop once you reach your goal.
It is free to download with optional Pro upgrades, needs no account and collects no data. It is not a medical device, so set your goal with your doctor's advice in mind.
Get Dropkin free on the App Store