How much water to drink, and when
What the evidence says about the water you need each day, how to spread it from the moment you get up until you go to bed, and how it changes with your goal. Reviewed 15 October 2026.
Summary
A healthy adult needs about 2 L of total water a day as a woman and 2.5 L as a man, or 1 ml for every kcal they burn or eat if that is more. About 20 % comes from food, so that means 1.6–2 L of drinks, plus your sweat on training days. It is best spread over your waking hours: a little more in the morning and with meals, little in the 2 hours before bed and never more than 1 L in an hour.
Suggested split of a rest day’s drinks. It is not a measured rule: it applies the principles below (spread it out, drink with meals, little before bed). On training days your sweat is added around the session.
| Goal | Total water a day | Drinks (examples) | What changes |
|---|---|---|---|
| Lose fat | EFSA reference or 1 ml per kcal you burn | 80 kg man: 2.2 L · 60 kg woman: 1.6 L | You eat less, so food brings less water; 500 ml before meals may help a little |
| Maintain | EFSA reference or 1 ml per kcal you burn | 2.2 L · 1.6 L | This is the baseline |
| Build muscle | EFSA reference or 1 ml per kcal you eat | 2.5 L · 1.8 L | More food and more training; creatine does not dehydrate you |
| Perform | The baseline + the sweat of every workout | 2.2 L · 1.6 L + 0.8–1.5 L per hour of training | Lose less than 2 % of your weight while training, without gaining weight from drinking |
Examples with an 80 kg man who burns 2,700 kcal and a 60 kg woman who burns 2,000 kcal, on a rest day. For building muscle, with 3,100 and 2,300 kcal plans.
How much water you need each day
There is no measured minimum for each person: guidelines give “adequate intakes”, amounts that cover almost all healthy people in moderate temperatures and activity. All of them refer to total water: any drink (water, coffee, tea, milk…) plus the water in food.
| Reference | Women | Men | Notes |
|---|---|---|---|
| EFSA 2010 (Europe) | 2.0 L/day | 2.5 L/day | Same for older adults. +300 ml in pregnancy and +700 ml while breastfeeding. For moderate activity (PAL 1.6) |
| IOM 2004 (US) | 2.7 L/day | 3.7 L/day | Based on what healthy people drink on average, not on a measured need |
| ESPEN 2018 (older adults) | 1.6 L of drinks | 2.0 L of drinks | Minimum for older people, who tend to drink too little |
- Food provides part of it. EFSA assumes 20–30 % of total water; in surveys it was 27 % in the UK and 36 % in France. Fruit, vegetables, soups and dairy provide more.
- The need rises with energy. At least 1 L of water is needed for every 1,000 kcal. So someone who burns 3,000 kcal needs about 3 L of total water, even if the general reference is lower.
- Everything else comes on top: exercise sweat, heat, pregnancy and breastfeeding.
How to spread it through the day
The body keeps no water in reserve: what you drink beyond your needs leaves in your urine within a few hours. That is why when you drink matters as much as how much. These are the principles with evidence behind them, and how to apply them.
- Spread it over your waking hours. The kidneys of a healthy adult can remove roughly 0.8–1 L of water per hour. Drinking much faster than that does not hydrate you more; in extreme cases, especially during exercise, it dilutes the sodium in your blood (hyponatremia). Never more than 1 L in an hour at rest.
- On waking. You have gone 7–9 hours without drinking, and first-morning urine is the most concentrated, which makes it the best one to check how you are doing. A glass or two (300–500 ml) is an easy way to start the day.
- With every meal. Drinking with meals is easy to remember and spreads your drinks naturally. If you want to lose fat, 500 ml half an hour before main meals led to a little more weight loss in two trials.
- Between meals, by thirst. In healthy adults, thirst is a good guide in daily life. Keeping a bottle nearby helps you not to forget.
- Little to drink in the 2–3 hours before bed. That makes getting up to pee less likely. Don’t drink less during the day to compensate: move your drinks earlier, don’t cut them.
- Caffeine early. Coffee counts as fluid in people who drink it daily, but 400 mg of caffeine even 6 hours before bed cut sleep by more than an hour. Better before mid-afternoon.
- Older adults: at set times. Thirst works less well with age, so it is worth drinking with every meal and in between even without feeling thirsty.
- In the heat, more often. Sweat goes up and the body takes 10–14 days to adapt to heat. Drink more often and add a little salt if you sweat a lot.
| When | How much (2.2 L) | How |
|---|---|---|
| On waking | 350 ml | One or two glasses |
| Morning, until lunch | 500 ml | Sips, with a bottle nearby |
| Lunch | 450 ml | With it, or 500 ml half an hour before if you want to lose fat |
| Afternoon | 450 ml | Between meals, especially if it is hot |
| Dinner | 350 ml | With it |
| Last 2 hours | 100 ml | Just sips if you are thirsty |
Example for 2.2 L of drinks (an 80 kg man who wants to lose fat). Tara works out yours from your goal in Habits → Water.
On training days
| When | What to do | Example (80 kg, 1 hour, 1 L/h of sweat) |
|---|---|---|
| Before | 5–7 ml per kilo at least 4 hours before; if you don’t pee or your urine is dark, 3–5 ml per kilo more about 2 hours before | 400–550 ml with the meal before |
| During | Drink so you lose no more than 2 % of your weight, without drinking more than you sweat | Up to 1 L in small sips |
| After | 1.5 L for every kilo lost, with some sodium (food or drink) | If you lose 0.5 kg: 750 ml |
Weighing yourself without clothes before and after a one-hour session gives your real sweat rate: weight before − weight after + what you drank, divided by the hours. Most athletes sweat 0.8–1.5 L per hour; in 1,303 athletes, from 0.8 L/h in baseball to 1.5 L/h in American football.
By goal
Lose fat
Base your water on what you burn, not on your reduced calories: eating less brings less water with food, and the difference has to be drunk. Drinking less does not speed up fat loss. The first drop in weight on a diet is partly water: each gram of glycogen is stored with about 3 g of water, and when you start a deficit, especially with few carbohydrates, the body uses glycogen and releases that water. A high-protein diet does not dehydrate you either: with 3.6 g/kg for 4 weeks, fluid balance did not change.
Maintain
The reference, or 1 ml per kcal you burn, is enough. If you work on your feet, walk a lot or it is hot, the ml per kcal raises the figure on its own. In the US, healthy adults drink on average 2.75 L (women) and 3.46 L (men) of total water: EFSA is a sensible minimum, not a ceiling.
Build muscle
In a surplus you eat more than you burn, so water follows what you eat: a 3,100 kcal plan asks for about 3.1 L of total water. Strength training adds its sweat. Creatine does not dehydrate you: a review of 10 trials found it does not worsen fluid balance or heat tolerance. As glycogen refills, part of the weight gained at first is water.
Perform
Sweat is what matters. Measure your rate by weighing yourself, drink before, during and after following the training-day table, and watch salt in long or hot sessions: sodium loss ranges from about 27 to 56 mmol per hour depending on the sport. In sessions over 4 hours or the first days of heat, 0.3–0.7 g of salt per litre of drink.
How to tell you are doing well
Three simple signs: your morning weight drops more than 1 % below usual, your urine is dark and you are thirsty. If two of them apply, you are probably short of water. First-morning urine is the most reliable to check; through the day it changes with what you have just drunk.
Risks of drinking too little and too much
- Mild dehydration. Losing 1.6 % of body weight in water worsened attention, working memory and fatigue in young men; in women, 1.4 % worsened mood and concentration and caused headaches. 2 % can already reduce performance, and more than 3 % raises the risk of heat illness.
- Drinking too much. Exercise-associated hyponatremia (sodium below 135 mmol/L) is mainly caused by drinking too much salt-free fluid for hours. In severe cases it causes brain swelling. The international consensus recommends drinking when thirsty and not gaining weight during exercise.
- With drinks available, people replace only about two thirds of their sweat, and more than half of athletes arrive at training already dehydrated.
Special situations
| Situation | Adjustment |
|---|---|
| Pregnancy | +300 ml of total water a day |
| Breastfeeding | +700 ml of total water a day |
| Older adults | At least 1.6 L (women) and 2 L (men) of drinks, at set times |
| Kidney stones | The US urology guideline asks for at least 2.5 L of urine a day, which usually means drinking more than usual: follow your doctor’s advice |
| Low-carbohydrate diets | The first days you lose the water stored with glycogen; watch thirst and urine, and add a little salt if you feel dizzy |
| Coffee | Counts as fluid in regular drinkers at moderate amounts; best kept away from bedtime |
| Kidney, heart or liver disease | There may be a fluid limit: your doctor sets the figure, not Tara |
How Tara calculates it
Total water = the higher of the EFSA reference (+ pregnancy or breastfeeding)
and 1 ml × the higher of what you burn and your kcal target
Drinks for the day = 80 % of total water
+ the sweat of what you log
+ the sweat of what is in today's calendar and not logged yet
Sweat per activity = your sweat per hour × hours × (METs ÷ 7), between 0.3 and 1.4 times
- Sweat is 0.6 L per hour at moderate effort (about 7 METs) by default, or the rate you measured in Habits → Water → “Measure your sweat”. It is scaled to the effort of each activity: walking adds less than running.
- What you plan in the calendar counts from the morning, so you can drink ahead; once you log the session, it replaces the plan. With the “fixed” target, if nothing is logged or planned that day, the daily average of your usual training is added.
- In Habits → Water, Tara splits your drinks with the template above (15 %, 25 %, 20 %, 20 %, 15 % and 5 %) so you can see how much goes with each part of the day.
- After training it suggests 1.25–1.5 L per kilo lost, and in long sessions it reminds you to drink by thirst and add salt.
- It is a guide, not something to force: thirst and urine colour are still good signals.
Sources
- EFSA 2010: dietary reference values for water
- CDC 2016: water intake in the US and IOM references
- ESPEN 2018: nutrition and hydration in older adults and summary of its figures
- Guelinckx et al. 2016: water from food and drinks
- Drewnowski et al. 2013: at least 1 L per 1,000 kcal
- Medical News Today: how much water the kidneys can remove per hour (approximate figure, no original study cited)
- Dennis et al. 2010: water before meals and weight loss
- Parretti et al. 2015: water before meals in obesity
- Continence Foundation of Australia: drinks and night-time urination
- Drake et al. 2013: caffeine 0, 3 and 6 hours before bed
- Killer et al. 2014: coffee and hydration
- ACSM 2007: exercise and fluid replacement (HKSI summary)
- NATA 2017: fluid replacement for the physically active
- NATA 2000: fluid replacement for athletes
- Barnes et al. 2019: sweat and sodium in 1,303 athletes
- Hew-Butler et al. 2015: consensus on exercise-associated hyponatremia
- Ganio et al. 2011: mild dehydration, attention and mood in men
- Armstrong et al.: mild dehydration in men and women (summary)
- Sekiguchi et al. 2021: weight, urine colour and thirst
- Martin et al. 2006: protein and hydration
- Fernández-Elías et al. 2015: water and muscle glycogen
- Lopez et al. 2009: creatine and hydration
- AUA: kidney stone guideline
General information for healthy adults. If you have kidney, heart or liver disease, or your doctor has limited your fluids, follow their advice.