# Water intake calculator: how much to drink in a day.

This water intake calculator starts from the adequate intakes set by EFSA in Europe and the US National Academies, then adds the sweat you lose in training, as a typical range or from your own weigh-in. Results are in litres or US fluid ounces, with every source listed below.

Use the calculator on the page: https://trainaq.com/tools/water-intake-calculator. For healthy adults 18 and over. An estimate, not medical advice. If you have kidney, heart or liver disease, take diuretics or have been told to limit fluids, follow your doctor’s advice instead. In pregnancy or while breastfeeding, use it as a guide to discuss with your midwife or doctor.

## How much water should I drink a day?

EFSA sets an adequate intake of 2.0 litres of total water a day for women and 2.5 litres for men; the US National Academies set 2.7 and 3.7 litres. Those totals include the water in food, about a fifth in US survey data, so drinks supply the rest. Training and heat add the sweat you lose.

- Adequate intakes from EFSA (2010) and the US National Academies (2005)
- Their own values for pregnancy and breastfeeding
- Training adds 0.5 to 2.0 litres an hour, the typical sweat loss of athletes
- Or your own sweat rate, from weighing yourself before and after training

## How does this water intake calculator work?

It works in three steps. It takes the adequate intake for an adult like you from EFSA or the US National Academies, splits it into drinks and food, then adds the sweat you lose in training: a typical range of sweat rates, or your own rate from a weigh-in before and after a session.

### 1. Start from an adequate intake

An adequate intake is an observed intake that keeps healthy people well hydrated, not an exact requirement. EFSA based its values on observed intakes and on how concentrated urine should be; the US National Academies on the median intake in a national survey. Both count every kind of drink and the water in food.

- EFSA: 2.0 litres for women, 2.5 litres for men
- US: 2.7 litres for women, 3.7 litres for men

### 2. Split drinks from food

Food supplies part of your water. In US survey data, drinks gave about 81% of total water and food about 19%. The US report states its drinks figures directly, and the calculator uses them; for EFSA it takes 80% of the total as drinks, the share the US report gives.

- Water, tea, coffee, milk and juice all count as drinks
- In pregnancy, food gave 22% of total water in the US data

### 3. Add the sweat you lose

Training adds the water you sweat out. Athletes typically sweat 0.5 to 2.0 litres an hour, so the calculator shows that range for your training time. If you have weighed yourself before and after a session, it uses your own rate instead, which fits you far better than a range.

- Heat, harder work and heavier clothing raise sweat loss
- More than 3 litres an hour is rare

### 4. Check it against your body

For most healthy people, thirst and drinks with meals keep hydration in balance from day to day. Urine colour is a rough check: darker when output is low, paler when it is high. Weighing yourself around training tells you what a session costs.

- Repeat the weigh-in in summer and winter: your rate changes with the weather

## Which numbers and formulas does the calculator use?

Water to drink is the drinks part of the adequate intake plus your training time times a sweat rate. The adequate intake comes from EFSA or the US National Academies. The sweat rate is either the typical range for athletes, 0.5 to 2.0 litres an hour, or your own rate from a weigh-in.

- Water to drink a day: `Drinks = AI drinks + T × S`
- Drinks part, EFSA values: `AI drinks = 0.8 × AI total`
- Total water a day: `Total = AI total + T × S`
- Your sweat rate from a weigh-in: `S = (W before − W after + F) ÷ hours`

- AI: adequate intake in litres a day; T: training time in hours
- S: sweat rate in litres an hour (typical range 0.5 to 2.0)
- W: body weight in kg, where 1 kg lost is about 1 litre of sweat; F: litres drunk in the session
- 1 litre = 33.8 US fluid ounces; a US cup is 8 fluid ounces

## What are the adequate intakes for adults?

EFSA sets 2.0 litres of total water a day for women and 2.5 for men, with 2.3 in pregnancy and 2.7 when breastfeeding. The US National Academies set 2.7 and 3.7 litres, with 3.0 in pregnancy and 3.8 when breastfeeding. Both count all drinks and the water in food.

| Adults | EFSA, total water | US, total water | US, from drinks |
| --- | --- | --- | --- |
| Women | 2.0 L | 2.7 L | 2.2 L (about 9 cups) |
| Men | 2.5 L | 3.7 L | 3.0 L (about 13 cups) |
| Pregnancy | 2.3 L | 3.0 L | 2.3 L (about 10 cups) |
| Breastfeeding | 2.7 L | 3.8 L | 3.1 L (about 13 cups) |

Sources: EFSA (2010), as summarised in EFSA’s Dietary Reference Values summary report (2017), Table 2; US Institute of Medicine (2005), Dietary Reference Intakes for Water, chapter 4. EFSA’s values hold for a moderate climate and moderate activity; the US values are for adults 19 and over.

## How much water do you lose in training and heat?

It varies widely between people and days. A review of athlete testing put typical sweat rates at 0.5 to 2.0 litres an hour. Heat, harder work and heavier clothing push it up: female competitive runners sweated about 0.7 litres an hour in temperate weather and 1.1 in warm weather in the same event.

| Who and where | Sweat rate | Source |
| --- | --- | --- |
| Athletes tested in the field, typical range | 0.5–2.0 L an hour | Baker 2017 |
| Female and male distance runners, temperate weather | About 0.7 and 1.0 L an hour | US National Academies 2005 |
| Male competitive runners, training or racing in heat | 1.0 to over 2.0 L an hour | US National Academies 2005 |
| Work in very hot (desert) climates | 0.3–1.2 L an hour | US National Academies 2005 |
| American football players, average | 1.51 L an hour | Barnes 2019 |
| Endurance athletes, average | 1.28 L an hour | Barnes 2019 |
| Basketball and soccer players, average | 0.95 and 0.94 L an hour | Barnes 2019 |

Averages from Barnes et al. (2019), 1,303 athletes tested from 2000 to 2017, with standard deviations of 0.38 to 0.70 litres an hour, so people in the same sport differ a lot. EFSA notes that losses in extreme heat and exercise can reach about 8 litres a day.

## What does a worked example look like?

Take a man who trains for 60 minutes a day. EFSA’s adequate intake is 2.5 litres, about 2.0 from drinks. At 0.5 to 2.0 litres of sweat an hour, his training adds 0.5 to 2.0 litres, so he drinks about 2.5 to 4.0 litres that day, or 85 to 135 US fluid ounces.

- He weighs 70.0 kg before a 60-minute session and 69.2 kg after, having drunk 0.5 litres: (0.8 + 0.5) ÷ 1 hour = 1.3 litres an hour
- At his own rate, the day’s drinks are 2.0 + 1.3 = 3.3 litres, about 112 fluid ounces
- A woman using the US values who trains for 90 minutes at 0.8 litres an hour: 2.2 + 1.2 = 3.4 litres from drinks

## How do I know if I am drinking enough?

For most healthy people, thirst and drinks with meals keep hydration in balance from day to day, the US report notes. Urine gives a rough check: it darkens when output is low and pales when it is high, though food, medicines and vitamins change its colour. Weighing before and after training shows what a session costs.

- Drinking somewhat less than the adequate intake is not necessarily a problem: healthy people stay hydrated over a wide range of intakes
- Over a few hours of hard work or heat, a water deficit can build up, so plan drinks for long sessions
- ACSM’s goal for drinking during exercise is to keep weight loss from sweating under 2% of body weight

## Can you drink too much water?

Yes. Healthy kidneys can pass only about 0.7 to 1.0 litres an hour, and drinking far beyond that can dilute the sodium in your blood, a dangerous condition called hyponatraemia. It is rare, but it has occurred in endurance events lasting many hours, from drinking too much or replacing too little sodium.

- Drink to replace what you lose, not more
- Drinks with electrolytes and carbohydrate can help over water alone in some situations, ACSM notes
- For events of many hours, plan both fluid and sodium

## Who should not use this water intake calculator?

Ask your doctor instead if you have kidney, heart or liver disease, take diuretics, or have been told to limit fluids. The calculator is for healthy adults. Children and teenagers under 14 have their own reference values, and the pregnancy and breastfeeding figures are a guide to discuss with your midwife or doctor.

- EFSA’s values assume a moderate climate and moderate activity
- Older adults keep the adult values, and thirst can be weaker with age, the US report notes

## How do coaches use water targets with clients?

Coaches turn the number into a daily habit. In Trainaq you give a client a water habit in glasses or millilitres on the days you choose. The client taps it up on their Today screen with a daily reminder, and you see their habit adherence over 7 and 28 days beside workouts and food logs.

- Change the target or pause the habit at any time without losing what was logged
- Add your own questions about thirst or training days to the client’s weekly check-in
- Steps and sleep habits sit beside water on the same Today screen

[Habit tracking in Trainaq](https://trainaq.com/features/habits)

## Sources

1. [EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on Dietary Reference Values for water. EFSA Journal. 2010;8(3):1459.](https://doi.org/10.2903/j.efsa.2010.1459)
2. [European Food Safety Authority. Dietary Reference Values for nutrients: summary report. EFSA Supporting Publications. 2017:e15121. (Section 3.5 and Table 2, water.)](https://doi.org/10.2903/sp.efsa.2017.e15121)
3. [Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: The National Academies Press; 2005. Chapter 4, Water.](https://doi.org/10.17226/10925)
4. [Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377–390.](https://doi.org/10.1249/mss.0b013e31802ca597)
5. [Baker LB. Sweating rate and sweat sodium concentration in athletes: a review of methodology and intra/interindividual variability. Sports Med. 2017;47(Suppl 1):111–128.](https://doi.org/10.1007/s40279-017-0691-5)
6. [Barnes KA, Anderson ML, Stofan JR, et al. Normative data for sweating rate, sweat sodium concentration, and sweat sodium loss in athletes: an update and analysis by sport. J Sports Sci. 2019;37(20):2356–2366.](https://doi.org/10.1080/02640414.2019.1633159)

## FAQ

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

Yes. The US National Academies found that the diuretic effect of caffeine appears to be short-lived, so coffee, tea and other caffeinated drinks count towards total water intake, as do milk and juice. Water is still the simplest choice for most of the day, since it brings no sugar or caffeine with it.

### Are eight glasses of water a day enough?

For some people. Eight 8-ounce glasses are about 1.9 litres. That is close to the drinks part of EFSA’s values, about 1.6 litres for women and 2.0 for men, but below the US figures of 2.2 and 3.0 litres from drinks, and it leaves out what you sweat in training.

### Why are the EFSA and US numbers different?

Both are adequate intakes drawn from what healthy people drink and eat, not exact requirements. The US values are median intakes from a US national survey; EFSA combined European intake data with how concentrated urine should be. Either is a fair starting point, and your thirst, urine and weigh-ins show which suits you.

### How much should I drink during a workout?

Enough to keep the weight you lose under about 2% of body weight, the goal ACSM sets for drinking during exercise, without drinking more than you sweat. Weigh yourself before and after a typical session to learn your rate, then drink part of it during the session and replace the rest afterwards.

### Do I need more water in hot weather even if I don’t train?

Yes. Both sets of values assume ordinary conditions, and the US report says people exposed to hot environments need more. Its estimates of daily fluid needs run from about 2 to 4 litres in a cool climate to far more in very hot ones, depending on how active you are and how long you are exposed.

### Does the calculator work for children or teenagers?

Only from 18. EFSA treats teenagers from 14 as adults for water, while the US report has separate values for ages 14 to 18, and younger children need much less. For a child or teenager, use those age-specific values or ask a paediatrician or dietitian, especially for a young athlete training in heat.

## Related

- [Habit tracking in Trainaq](https://trainaq.com/features/habits): Daily water, steps and sleep habits for clients
- [Heart rate zone calculator](https://trainaq.com/tools/heart-rate-zone-calculator): Your maximum heart rate and training zones
- [VO2 max calculator](https://trainaq.com/tools/vo2-max-calculator): Estimate fitness from a run, a walk or heart rate
- [TDEE calculator](https://trainaq.com/tools/tdee-calculator): Your maintenance calories, worked out

Source: https://trainaq.com/tools/water-intake-calculator