Daily Water Needs
How Many Liters of Water Should You Drink a Day?
The reference figures for daily water were written in liters to begin with. Here is what they say for women and men, what counts toward them, and what they mean for the water you keep in storage.
The National Academies put adequate total water at about 2.7 liters a day for women and 3.7 liters for men, from all drinks and food. About 80 percent usually comes from drinks, roughly 2.2 and 3.0 liters (calculated). It is a reference for healthy people, not a target, and most meet it by letting thirst guide them. For an emergency supply, store 1 U.S. gallon, about 3.8 liters, per person per day.
What you’ll learn
The short version
How many liters of water you should drink a day has a reference answer of about 2.7 liters of total water for women and 3.7 liters for men, counting drinks and food together.
- About 80 percent usually comes from drinks, including coffee and tea: roughly 2.2 liters for women and 3.0 for men (calculated).
- Needs vary with age, sex, pregnancy, breastfeeding, activity, heat and illness (CDC).
- One U.S. gallon is about 3.785 liters (NIST).
- Emergency storage: at least 1 gallon, about 3.8 liters, per person per day for at least 3 days (CDC).
Step 1
How many liters for women and for men
The liters of water a person takes in each day average about 2.7 for women and 3.7 for men among people who appear adequately hydrated, according to the National Academies.
The National Academies of Sciences, Engineering, and Medicine sets the Dietary Reference Intakes used in the United States. Its 2004 report on water found that women who appear to be adequately hydrated consume an average of about 2.7 liters (91 ounces) of total water each day, and men about 3.7 liters (125 ounces). Those figures became the adequate intake: a level judged enough for most healthy people, not a minimum and not a goal.
“Total water” is the key phrase. The report says about 80 percent of it comes from drinking water and beverages, including caffeinated beverages, and the other 20 percent from food. So the liters figure is not the same as liters of plain water from a tap or a bottle.
| Reference | Total water a day | From drinks, about 80% (calculated) | From food, about 20% (calculated) |
|---|---|---|---|
| Women | About 2.7 L (91 fl oz) | About 2.2 L | About 0.5 L |
| Men | About 3.7 L (125 fl oz) | About 3.0 L | About 0.7 L |
The same release says the vast majority of healthy people adequately meet their daily hydration needs by letting thirst be their guide. The Centers for Disease Control and Prevention (CDC), the federal public-health agency, does not publish one daily amount at all: its page About Water and Healthier Drinks says daily water intake recommendations vary by age, sex, pregnancy status, activity level and breastfeeding status. Whether you spell the unit liters, as in the United States, or litres, as in British English, the figures are the same.
The full picture in ounces and cups is in the guide to how much water a person should drink a day.
Step 2
What counts toward your liters of water a day
Your liters of water a day include every drink and the water in food, not only plain water, according to both the National Academies and the CDC.
The National Academies say people get water from juice, milk, coffee, tea, soda, fruits, vegetables and other foods and beverages. The CDC says daily water intake is mostly from water and other beverages, and that foods, especially those with high water content such as many fruits and vegetables, can also add to fluid intake. Its list of drinks that count includes plain water, milk, 100% juice, plain coffee or tea, and sparkling water.
That changes how a liter count should be read. The CDC’s consumption data show U.S. adults drank an average of 44 ounces of plain water a day in 2015–2018, which is about 1.3 liters (calculated). Against a 2.7 or 3.7 liter reference that looks low, but the gap is mostly other drinks and food.
Counting is not recommending. Every drink adds liters, but the CDC’s guidance still favours water and unsweetened drinks over sugary ones.
Step 3
Converting liters of water to cups, ounces and gallons
Converting liters of water to U.S. units uses fixed factors: one liter is about 33.8 fluid ounces or 4.2 cups, and one U.S. gallon is about 3.785 liters.
The factors come from the National Institute of Standards and Technology (NIST), the federal measurement agency. Its Handbook 44 tables give 1 U.S. gallon as exactly 128 fluid ounces and about 3.785 liters, 1 fluid ounce as about 29.573 milliliters, and 1 cup as exactly 8 fluid ounces. Every other number in the table is division.
| Liters | Fluid ounces | Cups (8 fl oz) | U.S. gallons |
|---|---|---|---|
| 0.5 L | 16.9 | 2.1 | 0.13 |
| 1 L | 33.8 | 4.2 | 0.26 |
| 2 L | 67.6 | 8.5 | 0.53 |
| 2.7 L (women, total water) | 91.3 | 11.4 | 0.71 |
| 3.7 L (men, total water) | 125.1 | 15.6 | 0.98 |
| 3.785 L (1 gallon) | 128 | 16 | 1.00 |
Half a liter is the familiar 16.9 fl oz single-serve bottle, which is why the bottles-per-day guide uses it as its standard size.
Four liters against one U.S. gallon
- 3.785 Lin one U.S. gallon (NIST)
- 0.215 Lby which four liters exceed one gallon (calculated)
Step 4
Liters calculator: a reference, converted
The liters calculator shows a published reference in liters, cups, ounces and gallons, and turns the emergency allowance into liters for your household.
Daily water in liters, and storage in liters
A converter, not a prescription. It does not tell anyone what to drink.
How this is worked out. The references are the National Academies’ total water (2.7 L women, 3.7 L men), 80 percent of those for drinks (2.16 and 2.96 L, calculated), and Ready.gov’s ¾ gallon of fluid (96 fl oz, about 2.84 L, calculated). Ounces are liters × 33.814, cups are ounces ÷ 8, gallons are ounces ÷ 128. Storage is people × days × 3.785 liters, from the CDC’s 1 gallon per person per day. All arithmetic.
What it will not calculate. No weight-based formula, and no figure for children, pregnancy, breastfeeding, illness, heat or exercise, because none of these sources publishes one. No verdict on whether any amount is right for you; a clinician’s figure replaces these.
Step 5
When the liters you need can change
The liters of water a person needs can rise with heat, physical activity, fever or stomach illness, pregnancy and breastfeeding, and the agencies name these factors without a liter figure for each.
Heat and activity. The CDC says your body needs more water in hot climates and when you are more physically active. The National Academies say very active people and people in hot climates may need more. For emergencies, Ready.gov says water needs can double in very hot temperatures.
Fever, diarrhea or vomiting. The CDC lists each of these as a time the body needs more water. They are also times to follow a clinician rather than a reference table.
Pregnancy, breastfeeding and age. The CDC lists all three among the factors that change daily recommendations. Ready.gov says children, nursing mothers and sick people may need more water. Children's amounts are a question for a pediatrician.
Some people are told to drink less. Certain heart and kidney conditions and some medicines come with a fluid limit. If a clinician has set one for you, that limit is your number, and no reference in liters overrides it.
None of the sources cited here publishes a liter amount for each factor, so this page does not invent one.
Step 6
Is two liters of water a day a rule?
Two liters of water a day is a popular round number, not an agency rule: none of the National Academies, CDC or Ready.gov pages cited here sets it.
Two liters is about 67.6 fl oz, or 8.5 cups (calculated), close to the familiar eight 8-ounce glasses, which come to 64 fl oz, about 1.9 liters (calculated). Both numbers are easy to remember. Neither matches how the reference is built. The National Academies figure is a total that includes food and every beverage, and it differs between women and men.
Two liters of plain water
01
More than the average
Two liters of plain water is more than the 1.3 liters U.S. adults drank on average in the CDC's data. Whether it is right for one person depends on the rest of their drinks and food (calculated).
Women, from drinks
02
About 2.2 liters
The women's drinks share is about 2.2 liters, counting coffee, tea, milk and juice. Two liters of plain water plus a morning coffee already reaches it (calculated).
Men, from drinks
03
About 3.0 liters
The men's drinks share is about 3.0 liters. A man drinking two liters of plain water is covering about two-thirds of it, with other drinks adding the rest (calculated).
A round number is a fine reminder to drink. It is not a measure of whether any particular person is drinking enough; the National Academies' answer to that is thirst.
Step 7
Emergency water storage in liters
Emergency water storage in liters starts from the CDC's allowance of at least 1 U.S. gallon per person per day, which is about 3.785 liters, for drinking and sanitation.
The CDC's page How to Create and Store an Emergency Water Supply says to store at least 1 gallon of water per person, per day, for 3 days, and to try to store a 2-week supply if possible. Ready.gov gives the same allowance and says it covers drinking and sanitation, which is why it is larger than the roughly 2.8 liters (¾ gallon, calculated) of fluid Ready.gov gives for a normally active person. A 3-day supply for one person is about 11.4 liters (calculated).
| Household | 3 days | 2 weeks | 2-week weight |
|---|---|---|---|
| 1 person | 3 gal · 11.4 L | 14 gal · 53 L | About 117 lb |
| 2 people | 6 gal · 22.7 L | 28 gal · 106 L | About 233 lb |
| 4 people | 12 gal · 45.4 L | 56 gal · 212 L | About 466 lb |
Ready.gov says needs can double in very hot temperatures, which would make the daily allowance 2 gallons, about 7.6 liters per person (calculated). It also says never to ration drinking water unless authorities order it. The CDC calls unopened, commercially bottled water the safest and most reliable source in an emergency, and says to keep stored water at 50°F to 70°F, out of direct sunlight and away from gasoline and pesticides.
To size a plan for your household, the emergency water calculator works out gallons, containers and weight, and the guide to how much emergency water your family needs covers heat, children and other adjustments. The guide to storing water long term covers containers and rotation.
Questions
Common questions about liters of water a day
These are the questions people most often ask when they measure their water in liters.
The National Academies reference is about 2.7 liters of total water a day for women and 3.7 liters for men, from all drinks and food. About 80 percent usually comes from drinks, roughly 2.2 and 3.0 liters (calculated). Most healthy people meet their needs by letting thirst guide them.
No agency page cited here sets a two-liter rule. Two liters of plain water is more than the roughly 1.3 liters U.S. adults drank on average in CDC data (calculated), and other drinks and food add to it. Whether it is enough depends on the person, the heat, activity and health.
One liter is about 33.8 U.S. fluid ounces, or about 4.2 cups of 8 fl oz, calculated from the NIST figure of 29.573 milliliters per fluid ounce. Half a liter is about 16.9 fl oz, the standard single-serve bottle.
One U.S. gallon is about 3.785 liters, according to NIST. That gallon is also the CDC's emergency storage allowance per person per day, for drinking and sanitation.
Yes. The National Academies say the drinks share of total water includes caffeinated beverages, and the CDC lists plain coffee or tea among the drinks that count toward daily fluid intake. Water-rich foods add to the day as well.
Store at least 1 U.S. gallon, about 3.785 liters, per person per day for at least 3 days, and a 2-week supply if possible, according to the CDC. That is about 11.4 liters per person for 3 days and 53 liters for 2 weeks (calculated).
Sources
Where these figures come from
Every figure on this page is quoted from, or calculated from, one of these sources, checked in September 2026.
- National Academies of Sciences, Engineering, and Medicine, news release on dietary reference intakes for water (February 11, 2004). nationalacademies.org — about 2.7 L (91 oz) of total water a day for women and 3.7 L (125 oz) for men; about 80 percent from drinking water and beverages, including caffeinated beverages, and 20 percent from food; thirst as a guide; very active people and those in hot climates may need more. Checked September 2026.
- Centers for Disease Control and Prevention, “About Water and Healthier Drinks” (reviewed March 5, 2026). cdc.gov — recommendations vary by age, sex, pregnancy status, activity level and breastfeeding status; more water in hot climates, with activity, fever, diarrhea or vomiting; drinks and water-rich foods count. Checked September 2026.
- Centers for Disease Control and Prevention, “Fast Facts: Data on Water Consumption” (reviewed January 19, 2024). cdc.gov — U.S. adults drank an average of 44 ounces of plain water a day in 2015–2018. Checked September 2026.
- Ready.gov, “Water.” ready.gov — about ¾ gallon of fluid a day for a normally active person; at least 1 gallon per person per day for drinking and sanitation; needs can double in very hot temperatures; children, nursing mothers and sick people may need more; never ration drinking water unless ordered by authorities. Checked September 2026.
- Centers for Disease Control and Prevention, “How to Create and Store an Emergency Water Supply” (reviewed June 27, 2025). cdc.gov — 1 gallon per person per day for 3 days; 2-week supply if possible; unopened commercially bottled water is the safest and most reliable source; store at 50°F–70°F away from sunlight, gasoline and pesticides. Checked September 2026.
- National Institute of Standards and Technology, Handbook 44 (2026), Appendix C, “General Tables of Units of Measurement.” nist.gov — 1 U.S. gallon = 128 fl oz = about 3.785 L; 1 fl oz = about 29.573 mL; 1 cup = 8 fl oz. Checked September 2026.
- U.S. Geological Survey, “Water Density.” usgs.gov — a gallon of water at 70°F weighs 8.329 pounds. Checked September 2026.
