Daily water has two numbers: what you drink and what you get with food
Ask how much water to drink in a day and the usual answer is "eight glasses" or "two liters". The US reference values from the National Academies (NASEM, 2004) separate two figures. For men 19 and older, total water is 3.7 L a day, and 3.0 L of that is beverages, drinking water included. For women 19 and older the figures are 2.7 L total and 2.2 L from beverages. The rest comes from the water in food, from fruit and vegetables to rice and soup.
The calculator above finds the reference for your sex and age, or for pregnancy or breastfeeding, and shows how much to drink and your total water. It also draws the same person against the South Korean, EU, Japanese and Indonesian standards, works out how much water you lost to sweat from your weight before and after exercise, and lets you log what you drink today in a row of cups. The old version of this tool multiplied body weight by 30 mL and then by an activity factor and a weather factor. That formula has no official standard behind it, so it was dropped.
How to use the calculator
- Pick a group and enter your age: choose male, female, pregnant or breastfeeding, then type your age. The calculator starts at 19; for ages 14 to 18, see the table below.
- Add your weight (optional): the daily reference does not depend on weight. If you enter it, you also see total water per kg of body weight and how much to drink before exercise. Switch between lb and kg at any time.
- Read the comparison: in each bar the dark part is beverages and the lighter part, out to the end of the bar, is total water with food.
- Exercise days: enter your weight right before and right after, the fluid you drank and the time, and you get the share of body weight lost and how much to replace.
- Spread it over the day and log it: enter your wake-up time and bedtime to split your daily amount into 2-hour glasses. Add mL by hand or tap the cup, can or bottle button and the glasses fill from the first one. A marker shows the current time, and the sentence below tells you how much is left for the block you are in. Glasses from past blocks that are not full get a dashed outline. The log stays in this browser only if you turn saving on.
The US reference: NASEM 2004 Adequate Intakes for water
The National Academies of Sciences, Engineering, and Medicine set water as an Adequate Intake. "Total water" counts everything from food and drink, and "beverages" includes drinking water (liters per day).
| Group | Total water (L) | Beverages (L) |
|---|---|---|
| Men 19 and older | 3.7 | 3.0 |
| Women 19 and older | 2.7 | 2.2 |
| Boys 14–18 | 3.3 | 2.6 |
| Girls 14–18 | 2.3 | 1.8 |
| Pregnancy | 3.0 | 2.3 |
| Breastfeeding | 3.8 | 3.1 |
In fluid ounces, 3.0 L of beverages is about 101 fl oz and 2.2 L is about 74 fl oz. NASEM gives pregnancy and breastfeeding as full values, not as an amount to add, so the calculator uses them as they stand. For reference, a standard 8 fl oz cup is 237 mL, so 2.2 L is a little over nine cups.
Why the numbers differ from country to country
Applied to the same adult aged 30 to 49, the standards give the following (mL per day). The gaps come from the population each one was based on and from how each splits "what you drink" from "total water". None of them is wrong.
| Standard | Men: drink | Men: total | Women: drink | Women: total |
|---|---|---|---|---|
| South Korea 2025 | 1,200 | 2,500 | 1,000 | 2,000 |
| United States NASEM 2004 | 3,000 | 3,700 | 2,200 | 2,700 |
| European Union EFSA 2010 | 2,000 | 2,500 | 1,600 | 2,000 |
| Japan, ministry-sponsored campaign | 1,200 | 2,200 | — | — |
| Indonesia AKG 2019 | — | 2,500 | — | 2,350 |
- South Korea: the 2025 Korean Dietary Reference Intakes list liquids (water, other drinks and milk) of 1,200 mL for men and 1,000 mL for women aged 30 to 49, with total water of 2,500 and 2,000 mL. That is a much smaller drinking share than the US figure.
- European Union: the European Food Safety Authority (EFSA) sets total water only: 2.5 L for men and 2.0 L for women. It assumes beverages usually contribute up to 80% of total water, and the drink column above is 80% of the total. Pregnancy adds 300 mL and lactation adds 700 mL. Adults over 65 keep the adult value.
- Japan: a campaign sponsored by the Ministry of Health, Labour and Welfare gives an adult man at rest 2.5 L a day, made up of 1.0 L from meals, 0.3 L produced inside the body and 1.2 L of drinking water. The table shows 2.2 L total, which leaves out the water the body produces so the rows are comparable.
- Indonesia: the 2019 AKG sets total water only, 2,500 mL for men and 2,350 mL for women aged 19 to 64, dropping to 1,800 and 1,550 mL at 65 to 80 and 1,600 and 1,400 mL above 80.
The water in food
The gap between total water and what you drink is made up by food. Water content per 100 g, from USDA FoodData Central, is below. A 200 g portion (about 7 oz) of cooked white rice holds roughly 137 mL of water, and 200 g of watermelon holds roughly 183 mL.
| Food | Water per 100 g |
|---|---|
| Cucumber, with peel, raw | 95.2 g |
| Tomato, raw | 94.5 g |
| Watermelon, raw | 91.4 g |
| Milk, whole | 88.1 g |
| Orange, raw | 86.8 g |
| Apple, with skin, raw | 85.6 g |
| White rice, cooked | 68.4 g |
If you eat plenty of soup, fruit and vegetables, food supplies more of your water. If you mostly eat dry foods such as bread and crackers, you will need to drink more to reach the same total.
Spreading it over the day
Once you know how much to drink, the next question is when. The Japanese campaign "Drink water for health", backed by the Ministry of Health, Labour and Welfare, advises drinking little and often to prevent heat illness, and having water when you wake up and after a bath, because you sweat a lot while asleep and while bathing. Healthy kidneys can excrete up to about 20 L of water a day. That is less than 1 L an hour, so drinking a large amount in a short time can leave extra water in the body and dilute the sodium in your blood.
The calculator splits the time from your wake-up time to your bedtime into 2-hour blocks and shares your daily amount out in proportion to each block's length. The running total at the end of each block is rounded to 10 mL and the last block makes up the exact goal, so the numbers above the glasses add up to your daily amount. This split is the calculator's own convention, not a timetable set by any official standard. For a man aged 19 or over (3.0 L of beverages under NASEM) who is awake from 7 AM to 11 PM, that is about 375 mL every 2 hours, shown as 380 mL and 370 mL in turn.
How much to drink on days you exercise
The American College of Sports Medicine (ACSM, 2007) notes that sweat loss varies widely, from 0.5 to 2.0 L an hour, depending on the person and the conditions. It therefore gives no single number and advises weighing yourself before and after to tailor your intake.
- Before: starting about 4 hours ahead, drink 5 to 7 mL per kg of body weight, slowly.
- During: drink so that you do not lose more than 2% of your body weight. Drinking so much that your weight goes up risks low blood sodium (hyponatremia).
- After: drink about 1.5 L for every kg of weight lost.
| Body weight | 4 hours before exercise | 2% of body weight |
|---|---|---|
| 110 lb | 250–350 mL | 2.2 lb |
| 130 lb | 290–410 mL | 2.6 lb |
| 155 lb | 350–490 mL | 3.1 lb |
| 175 lb | 400–560 mL | 3.5 lb |
| 200 lb | 450–640 mL | 4.0 lb |
For example, a woman who weighs 128.7 lb before a one-hour run, drinks 300 mL (about 10 fl oz) and weighs 127 lb afterward has lost 1.7 lb, or 1.3% of her body weight, which is under 2%. Her sweat loss is about 0.77 kg + 0.3 L = 1.07 L, so about 1.07 L an hour. After the run she can drink 0.77 × 1.5 ≈ 1.16 L (about 39 fl oz) over a few hours.
Common mistakes
- Treating total water as the amount to drink: the 2.7 L and 3.7 L NASEM figures include the water in food. The beverage amounts are 2.2 L and 3.0 L.
- Treating "body weight × 30 mL" as an official rule: the NASEM, EFSA and Korean standards are all set by sex and age and do not scale with weight.
- Leaving coffee and tea out: they are beverages and count toward your fluid intake. Check your caffeine separately.
- Waiting until you are thirsty: thirst weakens with age. EFSA notes that the kidneys' ability to concentrate urine and the sense of thirst decrease as people get older, yet it applies the adult value to older people too. Do not rely on thirst alone.
- Drinking until your weight goes up during exercise: drinking far more than you sweat out can dilute blood sodium.
Limits and cautions
- These values assume ordinary temperatures and ordinary activity. Heat, high altitude, hard exercise, fever and diarrhea all raise what you need.
- If a doctor has restricted your fluids because of kidney disease or heart failure, follow your doctor's instructions, not this calculator.
- The before-and-after exercise calculation treats 1 kg of weight as 1 L of water. It ignores anything that changed your weight through the toilet or through food.
- Age, weight, wake-up time and bedtime go only after the # when you copy the link, so they are never sent to a server. What you drink today and the two times stay in this browser only if you turn saving on.
Reference date Sources were checked on 2026-10-09; sources 04 and 08, used for spreading water over the day, were rechecked on 2026-10-19.
Sources
- 01NASEM: Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate (2004)Table S-2: total water and beverages, adults 19+, ages 14–18, pregnancy, lactation
- 02EFSA: Scientific Opinion on Dietary Reference Values for water (2010)Adults 2.0 L (women) and 2.5 L (men), beverages up to 80%, pregnancy +300 mL, lactation +700 mL
- 03Korean Nutrition Society: 2025 Korean Dietary Reference IntakesLiquids and total water, ages 30–49: men 1,200 and 2,500 mL, women 1,000 and 2,000 mL
- 04「健康のため水を飲もう」 poster (sponsored by Japan's Ministry of Health, Labour and Welfare)2.5 L a day = meals 1.0 L + produced in the body 0.3 L + drinking water 1.2 L
- 05Permenkes RI No. 28 Tahun 2019 (AKG)Water by age and sex: ages 19–64 men 2,500 and women 2,350 mL, 65–80 men 1,800 and women 1,550 mL, over 80 men 1,600 and women 1,400 mL
- 06ACSM Position Stand: Exercise and Fluid Replacement (Sawka et al., 2007)5–7 mL/kg four hours before, sweat 0.5–2.0 L/h, stay within 2% of body weight, about 1.5 L per kg lost afterward
- 07USDA FoodData Central (SR Legacy)Water per 100 g (FDC 168409, 170457, 167765, 171265, 169097, 171688, 168878)
- 08StatPearls: Hyponatremia (Rout, Afzal, 2026-06-19 update)Healthy kidneys can excrete up to about 20 L of water a day
Frequently asked questions
How much water should I drink a day?
The NASEM 2004 Adequate Intake for adults 19 and older is 3.7 L of total water for men and 2.7 L for women. Beverages, including drinking water, make up 3.0 L and 2.2 L of that. The rest comes from the water in food.
Is eight glasses of water a day correct?
Eight 8 fl oz glasses is about 1.9 L, which is below the NASEM beverage figure of 2.2 L for women and 3.0 L for men. Those figures count all beverages, not plain water alone, and total water also includes the water in food.
How much should I drink each hour while I'm awake?
Spread evenly over 16 waking hours (7 AM to 11 PM), the 3.0 L of beverages NASEM sets for men 19 and over comes to about 188 mL an hour, or about 375 mL every 2 hours. The 2.2 L for women comes to about 138 mL an hour. A campaign backed by Japan's health ministry advises drinking little and often, including when you wake up and after a bath.
Is multiplying body weight by 30 mL accurate?
The NASEM, EFSA and Korean water standards are all set by sex and age and do not scale with body weight. Weight times 30 mL is a rule of thumb with no official standard behind it, so this calculator does not use it.
Do coffee and tea count toward my water?
Yes. NASEM counts all beverages, including drinking water, toward the beverage amount. Coffee and tea contain caffeine, so check your daily caffeine separately.
How much more should I drink on days I exercise?
Sweat loss varies from 0.5 to 2.0 L an hour, so the most accurate method is to weigh yourself before and after. The American College of Sports Medicine advises drinking so that you lose no more than 2% of your body weight during exercise, and about 1.5 L for each kg lost afterward.
How much more do I need during pregnancy or breastfeeding?
NASEM gives full values: 3.0 L of total water, 2.3 L of it from beverages, in pregnancy, and 3.8 L total, 3.1 L from beverages, while breastfeeding. Choose Pregnant or Breastfeeding in the calculator to use them.
Can you drink too much water?
Yes. Drinking far more than you sweat out in a short time can dilute the sodium in your blood, a condition called hyponatremia. If your weight went up during exercise, you drank too much. People whose fluids are restricted for kidney disease or heart failure should follow their doctor's instructions.
Where is my daily log stored?
By default nowhere. Only if you turn the saving switch on are today's log and your wake-up time and bedtime kept in this browser. The log starts fresh at midnight, or at your bedtime if that is after midnight. Age, weight and the two times go only after the # in the link you copy, so they are never sent to a server.