# How much water to drink a day?

Gives the daily Adequate Intake of water from the National Academies (Institute of Medicine, 2005) for an age and sex, and during pregnancy or breastfeeding: total water and the part from drinks, in litres, cups, and fluid ounces.

- Page: https://www.acalculator.org/health/water-intake-calculator
- JSON spec: https://www.acalculator.org/health/water-intake-calculator.json
- Version: 516905881849

## Default answer

Example with the default inputs (Age 30, Sex Female, Pregnant or breastfeeding? Neither): Aim for about 2.2 L (9.3 cups) of drinks a day. With the water in food, that is 2.7 L of water in all.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| age | Age | Your age in whole years, from 1. |
| sex | Sex | Sex, which sets the intake from age 9. |
| stage | Pregnant or breastfeeding? | Pregnancy and breastfeeding have their own intakes, for ages 14 to 50. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| drinks | From drinks | Water to drink each day, including all beverages: the IOM figure for drinks. |
| cups | Cups of drinks | The water from drinks in US cups of 8 fluid ounces. |
| ounces | Fluid ounces of drinks | The water from drinks in US fluid ounces. |
| total | Total water | The Adequate Intake of total water per day: drinks plus water in food. |

## Method

Look up the Institute of Medicine Adequate Intake for the age, sex, and life stage: total water and the part from drinks, in litres per day; cups = litres ÷ 0.2365882365.

## Assumptions

- The intakes are the Institute of Medicine (2005) Adequate Intakes for healthy people, set from the median intakes of well-hydrated people in a US survey.
- Drinks include plain water and every other beverage, including coffee and tea; the rest of the total comes from food.
- People who are physically active or exposed to heat need more total water (IOM).
- Pregnancy and breastfeeding values apply to ages 14 to 50. This is general information, not medical advice.

## Worked examples

1. age = 30, sex = female, stage = none gives total = 0.0027, drinks = 0.0022, cups = 9.298856. Source: Institute of Medicine (2005), DRI for Water, chapter 4: women 19 to 30 years, 2.7 L/day total water, about 2.2 L (≈ 9 cups) from beverages.
2. age = 45, sex = male gives total = 0.0037, drinks = 0.003, cups = 12.680259. Source: Institute of Medicine (2005), chapter 4: men 31 to 50 years, 3.7 L/day total water, about 3.0 L (≈ 13 cups) from beverages.
3. age = 28, sex = female, stage = pregnant gives total = 0.003, drinks = 0.0023. Source: Institute of Medicine (2005), chapter 4: pregnancy, 3.0 L/day total water, about 2.3 L (≈ 10 cups) from beverages.
4. age = 25, sex = female, stage = breastfeeding gives total = 0.0038, drinks = 0.0031. Source: Institute of Medicine (2005), chapter 4: lactation, 3.8 L/day total water, about 3.1 L (≈ 13 cups) from beverages.
5. age = 15, sex = male gives total = 0.0033, drinks = 0.0026. Source: Institute of Medicine (2005), chapter 4: boys 14 to 18 years, 3.3 L/day total water, about 2.6 L from beverages.
6. age = 6, sex = female gives total = 0.0017, drinks = 0.0012. Source: Institute of Medicine (2005), chapter 4: children 4 to 8 years, 1.7 L/day total water, about 1.2 L from beverages.

## FAQ

### How much water should I drink a day?

For adults, the National Academies (Institute of Medicine, 2005) set an Adequate Intake of 2.7 litres of total water a day for women and 3.7 litres for men. About 80% comes from drinks: about 2.2 litres (9 cups) for women and 3.0 litres (13 cups) for men. The rest comes from food.

### Do coffee and tea count toward my water intake?

Yes. The National Academies count all beverages, including caffeinated ones, toward total water. They found that the diuretic effect of caffeine may be short-lived and that these drinks still add to your water intake.

### Do I need more water when I exercise or it is hot?

Yes. The Adequate Intakes are for typical daily life. People who are physically active or exposed to heat need more total water, and very active people in hot weather can need 6 litres or more a day. The American College of Sports Medicine suggests weighing yourself before and after exercise to see how much sweat you lose.

### How much water do I need when pregnant or breastfeeding?

The Adequate Intake rises to 3.0 litres of total water a day in pregnancy (about 2.3 litres, or 10 cups, from drinks) and to 3.8 litres when breastfeeding (about 3.1 litres, or 13 cups, from drinks), for ages 14 to 50.

### Is the 8 glasses a day rule right?

It is close for many women but low for many men. Eight 8-ounce glasses are 64 fluid ounces, or about 1.9 litres. The National Academies' figure for drinks is about 2.2 litres for women and 3.0 litres for men, and thirst and normal drinking at meals keep most healthy people hydrated.

### Can I drink too much water?

Yes, but it is rare. The National Academies set no upper limit, but note that healthy kidneys can excrete at most about 0.7 litres an hour. Drinking far more than that can cause water intoxication and low blood sodium (hyponatremia), which the National Academies note can be life threatening.

## Sources

- Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: The National Academies Press, 2005, chapter 4 (Water) and Summary. doi:10.17226/10925. https://www.nationalacademies.org/read/10925/chapter/6
- National Academies of Sciences, Engineering, and Medicine. Report sets dietary intake levels for water, salt, and potassium to maintain health and reduce chronic disease risk (news release, February 11, 2004).
- Sawka MN, Burke LM, Eichner ER, et al. American College of Sports Medicine position stand: Exercise and fluid replacement. Medicine and Science in Sports and Exercise 2007;39:377–390. doi:10.1249/mss.0b013e31802ca597
- NIST SP 811 (2008), Appendix B: 1 US gallon = 3.785411784 L exactly; 1 cup = 1/16 gallon = 8 fluid ounces = 0.2365882365 L.