ThirstyBotSplit your workout drinking into three parts. About 4 hours before, drink 5–7 ml per kg of body weight, which is about 11–16 oz for a 150 lb person. During the workout, sip about 7 oz (200 ml) every 15–20 minutes, or drink when you feel thirsty. Afterwards, replace 100–150% of the weight you lost, roughly 15–23 oz for every pound. The goal is to lose less than 2% of your body weight to sweat, without drinking so much that you weigh more after the session than before.
Is drinking water before a workout good or bad?
It’s good, as long as you do it early. The American College of Sports Medicine (ACSM) recommends starting exercise already well hydrated:
- About 4 hours before: drink 5–7 ml/kg. For a 150 lb (68 kg) person, that is about 340–475 ml (11–16 oz).
- About 2 hours before: if you still haven’t peed, or your urine is dark, drink another 3–5 ml/kg (about 205–340 ml, or 7–11 oz, at 150 lb).
Drinking early gives your body time to absorb what it needs and pass the rest before you start, so you are less likely to stop mid-session for the bathroom. There is no point gulping a lot right before you walk into the gym, either. The National Athletic Trainers’ Association (NATA) concluded that drinking more than you need before exercise does not improve performance.
Should you drink water during a workout?
Yes, but how much differs a lot between people. According to NATA, adults sweat anywhere from 0.5 to 4 liters (17 to 135 oz) an hour during exercise, depending on the person, the intensity and the weather. Two simple approaches:
- Drink about 200 ml (7 oz) every 15–20 minutes, a rate NATA considers suitable for many people.
- Or drink to thirst. NATA and the international consensus on exercise-associated hyponatremia both treat this as a safe way to avoid overdrinking.
If you train outdoors in the heat, you will sweat more, so drink more steadily.
Weigh yourself to see how much you sweat
ACSM and NATA both use this method to estimate an individual’s sweat loss. Weigh yourself just before your workout and again right after, dried off and in the same clothes. Almost all the weight you lose in one session is sweat, and 1 kg is about 1 liter (1 lb is about 15 oz).
- You lost less than 2% of your body weight (under 3 lb if you weigh 150 lb): you drank enough during the session.
- You lost 2% or more: drink more during your next workout.
- You weigh more than before: you drank more than you sweated. Drink less next time.
How much water to drink after a workout
NATA recommends replacing 100–150% of the fluid you lost and eating and drinking again within 2 hours. For example, if you lost 2 lb, drink about 31–46 oz (0.9–1.4 liters).
Spread this over a few hours instead of downing it at once. Healthy kidneys can only clear about 0.8–1 liter (27–34 oz) of water an hour, so drinking faster does not rehydrate you any faster.
No scale? Drink to thirst and check your urine. Pale straw yellow (levels 1–3 on the 8-colour urine chart) means you are hydrated.
Sample hydration schedule for a workout day
For a 150 lb (68 kg) person with a 1-hour workout at 5:30 pm:
| Time | Amount | Notes |
|---|---|---|
| 1:30 pm | 11–16 oz (340–475 ml) | About 4 hours before (5–7 ml/kg) |
| 3:30 pm | 7–11 oz (205–340 ml) | Only if you haven’t peed or your urine is dark |
| 5:30–6:30 pm | ~7 oz (200 ml) every 15–20 min | Or drink to thirst |
| 7:00–9:00 pm | 100–150% of the weight you lost | Spread out, with dinner |
Outside these times, drink as you normally would. For a full-day plan, see the water drinking schedule.
What to drink: water, sports drinks, milk or coconut water?
- Water: enough for most workouts.
- Sports drinks (carbohydrate and electrolytes): according to NATA, they may help when a session lasts longer than 1 hour or includes a lot of high-intensity intervals. For shorter workouts, water is enough.
- Milk: in a trial of 72 men, whole and skim milk were retained longer than water, similar to an oral rehydration solution. Note that the trial was done at rest, not after exercise.
- Coconut water: a small study of 12 men found coconut water rehydrated no better or worse than water or a sports drink after exercise, but the men reported more bloating and stomach upset with it.
- If you sweat heavily (long sessions, hot weather): NATA advises a rehydration drink that contains enough sodium, not just plain water.
Is drinking cold water after a workout bad?
Not for healthy people. NATA notes that athletes tend to prefer cool, flavored drinks and recommends having them available so people drink enough. None of the sources we used advise avoiding cool water after exercise. What matters more is drinking enough and spreading it out.
Can you drink too much water while exercising?
Yes. If you drink more than you sweat during a long session, the sodium in your blood gets diluted. This is called hyponatremia, and signs include nausea, headache, confusion and tiredness. Two simple rules: don’t finish a workout heavier than you started, and don’t drink more than about 1 liter (34 oz) an hour.
Log your workouts in ThirstyBot
On the home screen, tap Workout and enter how long you trained. The app adds water to today’s goal and suggests what to drink before, during and after, with the pre-workout amount already worked out from your weight. For your everyday baseline, see how much water should I drink a day or try the water intake calculator.
ThirstyBot does not replace medical advice. If you have a medical condition, ask your doctor how much water is right for you.
Sources
- ACSM – Position Stand: Exercise and Fluid Replacement (Sawka et al., 2007)
- Hong Kong Sports Institute – Water, the fountain of life (summary of ACSM 2007)
- NATA – Position Statement: Fluid Replacement for the Physically Active (2017)
- Hew-Butler et al. – Third International Exercise-Associated Hyponatremia Consensus, BJSM (2015)
- Maughan et al. – Beverage hydration index, Am J Clin Nutr (2016)
- Kalman et al. – Coconut water vs a sports drink, J Int Soc Sports Nutr (2012)
- Dmitrieva et al. – eBioMedicine 92:104638 (2023)
- MedlinePlus (U.S. National Library of Medicine) – Low blood sodium
- HPRC – How to accurately assess hydration status using urine color charts
