Water intake calculator: US and EU daily references
Choose your group and the calculator shows how much total water a day the US National Academies (NASEM) and the European Food Safety Authority (EFSA) publish as adequate for healthy people like you, and how much of it usually comes from drinks. The figures are published references for groups of people, not a personal target. Heat, exercise and illness raise the need for water.
Published water references
Choose a group to see the published references.
On a GLP-1 medicine
Vomiting and diarrhea lose fluid. The Wegovy and Zepbound labels warn of kidney injury from dehydration and advise patients to take precautions to avoid fluid depletion. Tell your prescriber about nausea, vomiting or diarrhea that does not stop.
US prescribing information for Wegovy (section 5.5) and Zepbound (section 5.3).
These are published references for healthy people in your group, not a prescription for you. Heat, exercise and illness raise the need for water.
Where do the numbers come from?
Both bodies set an Adequate Intake (AI) for total water: drinking water, every other drink, and the water in food. An AI is the amount that healthy people in a group usually take in. It is not a minimum, and it is not a requirement for any one person. NASEM says plainly that the AI "should not be interpreted as a specific requirement", and that people who are physically active or in hot places need more. EFSA's values apply to moderate temperatures and moderate activity.
The two bodies looked at different surveys and came to different figures:
Where do the numbers come from?
Group
US total water (NASEM)
US from drinks (NASEM)
EU total water (EFSA)
EU from drinks (80% of the total)
Women, 19 and older
2.7 L
2.2 L
2.0 L
1.6 L
Men, 19 and older
3.7 L
3.0 L
2.5 L
2.0 L
Pregnancy
3.0 L
2.3 L
2.3 L
1.8 L
Breastfeeding
3.8 L
3.1 L
2.7 L
2.2 L
NASEM states the drinks amount for each group itself. EFSA assumes that drinks usually supply about 80% of total water and food the other 20%, so the EU drinks column is 80% of EFSA's total. EFSA gives pregnancy and breastfeeding as an increase on the 2.0 L for women: 0.3 L more a day in pregnancy and about 0.7 L more while breastfeeding. The table adds that increase to 2.0 L.
A worked example
This example is illustrative. A woman of 35 who is not pregnant chooses Female and Neither. The calculator shows:
United States (NASEM): 2.7 L of total water a day, about 2.2 L of it from drinks.
European Union (EFSA): 2.0 L of total water a day, about 1.6 L of it from drinks.
If she chooses Pregnant instead, the US figure becomes 3.0 L (about 2.3 L from drinks) and the EU figure becomes 2.3 L, which is 2.0 L plus 0.3 L for pregnancy. The rest of the water comes from food: fruit, vegetables, soup and other foods with a lot of water in them.
Litres, fluid ounces and cups
The US figures are often quoted in ounces or cups. The calculator uses the exact US fluid ounce (29.5735295625 mL) and the US cup of 8 fluid ounces (236.5882365 mL), as NIST defines them, and rounds to one decimal:
Litres, fluid ounces and cups
Litres
US fluid ounces
US cups (8 fl oz)
2.0 L
67.6 fl oz
8.5 cups
2.2 L
74.4 fl oz
9.3 cups
2.5 L
84.5 fl oz
10.6 cups
2.7 L
91.3 fl oz
11.4 cups
3.0 L
101.4 fl oz
12.7 cups
3.7 L
125.1 fl oz
15.6 cups
3.8 L
128.5 fl oz
16.1 cups
US nutrition labels use a rounder cup of 240 mL and an ounce of 30 mL, so a label-based figure can differ by a few percent. A UK (imperial) fluid ounce is smaller, about 28.4 mL.
Water on a GLP-1 medicine
Nausea, vomiting and diarrhea are among the most common side effects of GLP-1 medicines such as semaglutide and tirzepatide, and vomiting and diarrhea lose fluid. The US labels of Wegovy® (§ 5.5) and Zepbound® (§ 5.3) warn about acute kidney injury due to volume depletion: most reported cases were in people whose stomach side effects led to dehydration. The labels advise patients to take precautions to avoid fluid depletion, and to tell their healthcare provider about nausea, vomiting or diarrhea that is persistent.
The labels do not give a separate water amount for people on these medicines. The references above are for healthy people. If you are often sick or have diarrhea, ask your prescriber how much to drink.
Frequently asked questions
How much water should a woman drink a day?
NASEM's reference for adult women is 2.7 L of total water a day, of which about 2.2 L usually comes from drinks. EFSA's reference is 2.0 L of total water, about 1.6 L of it from drinks. Both are references for healthy women in moderate conditions, not a personal target.
How much water should a man drink a day?
NASEM's reference for adult men is 3.7 L of total water a day, about 3.0 L of it from drinks. EFSA's is 2.5 L, about 2.0 L of it from drinks.
How many ounces is 2.7 liters?
2.7 L is 91.3 US fluid ounces, or 11.4 US cups of 8 fl oz. 3.7 L is 125.1 US fluid ounces, or 15.6 cups.
Does coffee or tea count?
Yes. Both NASEM and EFSA count all drinks and the water in food as part of total water. NASEM's drinks figures include "total beverages, including drinking water".
Why are the US and EU figures different?
They come from different data and different methods. NASEM based its values on what healthy people took in, in a US national survey. EFSA based its values on European data and its own assumptions, such as the 80% share from drinks. Neither is more correct for one person: both are references for groups.
Is there an upper limit?
NASEM did not set a Tolerable Upper Intake Level for water. It notes that the kidneys of a healthy adult can excrete at most about 0.7 to 1.0 L an hour.