Daily Water Intake Reference
See the Adequate Intake for total water for adult men and women from the U.S. Dietary Reference Intakes.
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How to read the result
- The Institute of Medicine (now the National Academy of Medicine) set an Adequate Intake (AI) for total water: 3.7 liters a day for men and 2.7 liters a day for women ages 19 and older.
- This is total water from drinking water, beverages and food. The report says the AI includes about 3.0 liters (about 13 cups) as total beverages, including drinking water, for men and about 2.2 liters (about 9 cups) for women.
- In the U.S. survey data the report used for ages 19 to 30, water in food provided about 19 percent of total water intake (0.7 liters a day for men and 0.5 liters for women). That split is not stated as a rule for every age.
- The report says the AI should not be interpreted as a specific requirement: for a healthy person a wide range of intakes is compatible with normal hydration. Higher intakes are needed by people who are physically active or exposed to hot environments. No upper limit was set for water, although the report notes that acute water toxicity has been reported after rapid consumption of very large quantities of fluid.
- The CDC page on water gives no single number. It says daily water intake recommendations vary by age, sex, pregnancy status, activity level and breastfeeding status, and that foods and other beverages count toward your total.
Adequate Intake of total water (liters per day)
| Group | Total water | of which beverages incl. drinking water |
|---|---|---|
| Men 19 and older (19-30, 31-50, 51-70, over 70) | 3.7 L | about 3.0 L (about 13 cups) |
| Women 19 and older (19-30, 31-50, 51-70, over 70) | 2.7 L | about 2.2 L (about 9 cups) |
Source: Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate (Institute of Medicine), chapter 4, Total Water AI summaries for ages 19 through 50 and 51 and older. The report lists the same value for every adult age group.
What "Adequate Intake" means
The figures on this page are Adequate Intakes (AI) for total water from the Institute of Medicine, now the National Academy of Medicine. The report sets the AI to prevent the harmful, mostly short-term (acute) effects of dehydration. It bases the AI on the median total water intake in U.S. survey data, because normal hydration can be kept over a wide range of intakes.
The report explains why it is an AI and not an average requirement. It says there is no single level of water intake that would ensure adequate hydration and optimal health for half of all apparently healthy persons in all environmental conditions, so an AI is established instead of an average requirement.
It also says that for a healthy person, daily consumption below the AI may not confer additional risk, and that the AI should not be interpreted as a specific requirement.
The values are 3.7 liters a day for men and 2.7 liters a day for women, ages 19 and older. The report lists the same value for 19 to 30, 31 to 50, 51 to 70 and over 70. For older adults it set the AI from the median intake of young adults, so that total water intake is not limited if the ability to respond to thirst declines.
"Total water" is not just what you drink
Total water means water from drinking water, beverages and food. The report says the AI includes about 3.0 liters (about 13 cups) as total beverages, including drinking water, for men and about 2.2 liters (about 9 cups) for women.
In the U.S. survey data used for ages 19 to 30, fluids provided about 81 percent of total water intake and water in food about 19 percent, which is 0.7 liters a day for men and 0.5 liters for women. The report does not state that split as a rule for every age.
The arithmetic is consistent: 3.0 + 0.7 = 3.7 liters for men, and 2.2 + 0.5 = 2.7 liters for women.
The report's cup figures are rounded. Using the report's own conversion factors (1 L = 33.8 fluid oz; 1 cup = 8 fluid oz), 3.0 L is about 12.7 cups, and 2.2 L is about 9.3 cups.
The U.S. Centers for Disease Control and Prevention (CDC) gives no single number on its water page. It says recommendations vary by age, sex, pregnancy status, activity level and breastfeeding status, that foods and other beverages add to fluid intake, and that plain drinking water counts toward your total.
Reading the numbers: worked examples
Water is a reference page, not a calculation, so these examples show how to read the table. The calculator displays what is in the report for the sex you choose and highlights the matching row.
Example 1, a woman of 35. The AI for women 31 to 50 is 2.7 L of total water. Of this, about 2.2 L (about 9 cups) is the report's figure for total beverages, including drinking water. The remaining part, roughly 0.5 L in the survey data for women 19 to 30, came from food.
Example 2, a man of 72. The AI for men over 70 is 3.7 L of total water, the same as for men 19 to 70. The report did not set a lower number for older adults. Beverages including drinking water are about 3.0 L (about 13 cups).
Example 3, a misreading. "3.7 liters of water" is not the same as "3.7 liters to drink." The report counts water from food in the total. We found no "8 glasses a day" rule in the report or on the Centers for Disease Control and Prevention (CDC) page we read.
More water, and a few cautions
The report says higher intakes of total water are required for those who are physically active or exposed to hot environments. A later section repeats that physical activity and environmental exposure increase water losses and therefore daily fluid needs.
The U.S. Centers for Disease Control and Prevention (CDC) lists times when your body needs more water: in hot climates, when more physically active, with a fever, and with diarrhea or vomiting. It says drinking water can prevent dehydration, which may cause unclear thinking, mood change, overheating, constipation and kidney stones.
The report did not set an upper intake limit for water because healthy people have a considerable ability to excrete excess water. It adds that acute water toxicity has been reported after rapid consumption of large quantities of fluid that greatly exceeded the kidney's maximal excretion rate of approximately 0.7 to 1.0 liters per hour.
On coffee and tea, the report says caffeinated beverages appear to contribute to total water intake in a similar way to noncaffeinated beverages. It counts total beverages, including drinking water, toward the AI.
Limits and what to discuss with a professional
We did not find, in the sources we read, a separate figure for people with kidney, heart or other conditions. If a clinician has told you to limit or increase fluids, follow that advice. This page cannot replace it.
We deliberately do not give a weight-based formula, such as a fixed number of milliliters per kilogram. The report does not give a formula based on body weight, and we found no official source in our set that does.
The calculator has only one input, the sex selection, so it always shows a result. The U.S. Centers for Disease Control and Prevention (CDC) mentions pregnancy and breastfeeding as factors that change recommendations, but the values on this page are the report's figures for men and women 19 and older generally.
Questions to bring to a health care professional: whether your medicines or conditions change how much fluid is right for you, and how much more to allow in heat or when you exercise. This page is general information, not medical advice.
How it is calculated
Adequate Intake of total water, adults 19 and older (all adult age groups in the report, 19 to 30, 31 to 50, 51 to 70 and over 70, have the same value):
Men: 3.7 L/day total, including about 3.0 L (about 13 cups) as beverages, including drinking water
Women: 2.7 L/day total, including about 2.2 L (about 9 cups) as beverages, including drinking water
The report does not give a formula based on body weight.
Frequently asked questions
Do I have to drink 8 glasses of water a day?
The reports and pages we read give no "8 glasses" rule. The Adequate Intake is for total water, including water from food and other beverages, and the report says it should not be read as a specific requirement.
Does coffee or tea count?
The report counts total beverages, including drinking water, toward the AI, and says caffeinated beverages appear to contribute to total water intake in a similar way to noncaffeinated beverages. The CDC says plain drinking water counts toward total water intake and that other beverages and water-rich foods also add to it.
What about hot weather or exercise?
The report says people who are physically active or exposed to hot environments need higher intakes. The CDC lists hot climates, more physical activity, fever, diarrhea or vomiting as times when your body needs more water.
I have kidney or heart disease.
If a clinician has told you to limit or increase fluids, follow that advice. This reference cannot replace it.
Sources and check date
- Institute of Medicine (now National Academy of Medicine): Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate
Chapter 4 Water: summary and Total Water AI summaries for ages 19 through 50 and 51+ · Published by the National Academies Press (cited as 2005) - CDC: About Water and Healthier Drinks
Meeting your water intake every day · Reviewed 2026-03-05
Date we opened and read the official sources: 2026-11-09. Guidance can change, so check the original before making an important decision.