How Much Water Should I Drink a Day?

How much water should you drink a day?

Most healthy adults do well with about 2.2 liters (9 cups) of drinks a day for women and 3.0 liters (13 cups) for men, according to the National Academies of Sciences, Engineering, and Medicine. These figures come from its 2004 report, which set an adequate intake (AI) for total water, meaning water from all drinks and food.

An AI is not a strict requirement. It is the typical intake of healthy people, and the report notes that most people meet their needs by drinking when thirsty and with meals. Food supplies roughly 20% of total water, and the rest comes from drinks. During pregnancy the beverage figure is about 2.3 liters (10 cups).

How do you calculate water intake by body weight?

Multiply your weight in pounds by 0.5 to get fluid ounces, add 12 ounces for every 30 minutes of exercise, and add 8 ounces for warm weather or 16 for hot or humid weather. That is the formula our water intake calculator uses. It is a widely quoted rule of thumb, not an official guideline, and it uses the same formula for men and women.

Worked example: a 160-pound person who exercises 30 minutes a day in a temperate climate gets 160 × 0.5 = 80 ounces for body weight plus 12 for exercise. That totals 92 fluid ounces, about 2.72 liters or 11.5 cups. A 200-pound person with the same routine gets 112 fluid ounces, about 3.31 liters or 14 cups.

Both results run above the National Academies' beverage figures, and they do not subtract the water in your food. Treat the weight-based number as an upper planning figure, and let thirst and urine color tell you whether you need that much.

Is eight glasses of water a day right?

Eight 8-ounce glasses is a reasonable habit but not a scientific requirement. It adds up to 64 ounces, or about 1.9 liters, which is less than the National Academies' beverage figures for both men and women.

A 2002 review in the American Journal of Physiology by Heinz Valtin looked for scientific evidence behind the "8 × 8" advice and did not find it for healthy adults in temperate climates who are not very active. Since other drinks and food also count, many people reach their total without drinking eight glasses of plain water.

How much water should you drink every day to lose weight?

There is no official higher water target for weight loss, so aim for the same daily amount as anyone else: about 2.2 liters of drinks for women and 3.0 for men, or more if you exercise. What helps is replacing drinks that contain calories. The CDC notes that water has no calories, so swapping sugary drinks for it can reduce your total intake.

The math is simple. Replacing 100 calories of sugary drinks a day saves 700 calories a week, about 0.2 pound by the 3,500-calorie rule of thumb, as long as you do not eat those calories elsewhere. Weight loss still depends on your overall calorie balance, which you can work out in our guide on how many calories to eat to lose weight or with the calorie deficit calculator.

Be wary of any plan that uses very large amounts of water to curb hunger, or of "water fasts" and cleanses. Scale changes from fluid shifts are not fat loss, and the risks of overdrinking are covered below.

How much more water do you need when you exercise or it's hot?

Add about 12 ounces (355 mL) for every 30 minutes of exercise and 8 to 16 ounces for warm or hot weather, then adjust for how much you sweat. These are the allowances in our calculator. For example, the 160-pound person who exercises 60 minutes in hot or humid weather gets 120 fluid ounces, about 3.55 liters or 15 cups.

Sweat rates vary widely, so individual plans work better than fixed numbers. The American College of Sports Medicine's position stand on fluid replacement says the goal during exercise is to prevent a loss of more than 2% of body weight from water deficit. Weighing yourself before and after a long session shows how much you lost; for a 160-pound person, 2% is 3.2 pounds. Drinks with electrolytes can help during long, sweaty sessions.

How can you tell if you're drinking enough?

Pale yellow urine and rarely feeling thirsty are the simplest everyday signs that you are drinking enough. Dark yellow urine, thirst and headache can suggest you need more.

Older adults may feel less thirsty, so regular drinking habits matter more with age. Some medications and supplements change urine color, so color is a guide rather than a measurement. Carrying a refillable bottle and having a drink with each meal is usually enough to stay on track.

Can you drink too much water?

Yes. Drinking very large amounts in a short time can dilute the sodium in your blood, a dangerous condition called hyponatremia. It is uncommon, and it is seen most often in endurance athletes who drink well beyond what they lose in sweat. The National Academies did not set an upper limit for water, but that does not mean any amount is safe in a short period.

People with heart failure or kidney disease may be told to limit fluids, and that advice overrides any calculator or guideline here. Pregnancy and breastfeeding raise needs, so check with your care team if you are unsure.