Water: how much should you really drink?
Nutrition
Key points
- National Academies: about 3.7 L (men) and 2.7 L (women) of total water a day from all sources.
- Food provides about 20% to 30% of your fluid.
- Even mild dehydration can affect concentration and mood.
- Replacing sugary drinks with water cuts calories.
How much you need
The National Academies of Sciences, Engineering, and Medicine set “adequate intake” for total water, from drinks and food combined, at about 3.7 liters (125 oz) a day for men and 2.7 liters (91 oz) for women. The European Food Safety Authority recommends about 2.5 liters for men and 2.0 liters for women from all sources (EFSA, 2010). Needs rise with heat, physical activity, pregnancy and breastfeeding.
What the research says
A review of studies found that water affects many body functions, and even mild dehydration (a loss of 1% to 2% of body weight) can impair concentration, mood and physical performance (Popkin et al., 2010).
Choosing water instead of sugary drinks is one of the easiest ways to cut calories and lower diabetes risk (Imamura et al., 2015).
Where “8 glasses a day” came from
There is no clear scientific source for the rule of eight 8-ounce glasses. It ignores the water in food and other drinks and differences in body size and activity.
Practical guide
- Drink when you are thirsty and with meals.
- Pale yellow urine usually means you are drinking enough.
- In hot weather or during exercise, drink more and do not wait until you are very thirsty.
- Older adults should drink on a schedule, because thirst weakens with age.
- Keep a reusable water bottle with you.
Frequently asked questions
Do coffee and tea count?
Yes. Moderate amounts of coffee and tea contribute to your fluid intake; their mild diuretic effect is small.
Can you drink too much water?
Yes, though it is rare. Drinking very large amounts in a short time, for example during endurance events, can cause dangerously low sodium (hyponatremia).
Sources
- EFSA Panel on Dietetic Products, Nutrition, and Allergies (2010). Scientific Opinion on Dietary Reference Values for water. EFSA Journal 8(3). doi:10.2903/j.efsa.2010.1459
- Popkin et al. (2010). Water, hydration, and health. Nutrition Reviews 68(8):439-458. doi:10.1111/j.1753-4887.2010.00304.x
- Imamura et al. (2015). Consumption of sugar sweetened beverages, artificially sweetened beverages, and fruit juice and incidence of type 2 diabetes: systematic review, meta-analysis, and estimation of population attributable fraction. BMJ :h3576. doi:10.1136/bmj.h3576
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