How the estimate is built
The baseline uses the European Food Safety Authority's adequate intakes for total water from all sources and assumes about 80% of it comes from drinks. Training and climate needs are added on top.
Hydration for lifters
Even modest dehydration, around 2% of body weight, has been linked to reduced endurance and, in some studies, lower strength and power output. For most gym sessions under an hour, drinking water to thirst is enough. For long or very sweaty sessions, adding sodium (from food or an electrolyte drink) helps you hold on to the fluid you drink.
The sweat test
- Weigh yourself (minimal clothing) right before training.
- Train as normal and note how much you drink.
- Towel off and weigh yourself again.
- Sweat loss (L) ≈ weight lost (kg) + fluid drunk (L). Divide by hours to get your sweat rate.
Frequently asked questions
How much water should I drink per day?
The European Food Safety Authority sets adequate total water intake at 2.5 L/day for men and 2.0 L/day for women, from all drinks and food. Usually 70–80% of that comes from drinks, which works out to about 2.0 L (men) and 1.6 L (women) of fluids before you add exercise and heat.
How much water should I drink during a workout?
The American College of Sports Medicine recommends drinking enough to avoid losing more than about 2% of body weight during exercise, without over-drinking. Sweat rates vary widely (roughly 0.3–2.4 L per hour), so weighing yourself before and after training is the best way to learn your own needs.
Do coffee and tea count toward water intake?
Yes. Moderate amounts of caffeinated drinks count toward your daily fluid intake, and caffeine's mild diuretic effect is smaller in people who drink it regularly. Food also supplies about 20% of total water on average.
Can you drink too much water?
Yes. Drinking very large volumes, especially during long endurance events, can dilute blood sodium and cause hyponatremia, which can be dangerous. Drink to thirst and to the volumes your sweat losses justify, and include sodium during long, sweaty sessions.
How can I tell if I am hydrated?
Pale-yellow urine, rarely feeling thirsty and a stable morning body weight are simple practical indicators. Dark urine and a drop of more than 1% of body weight after training suggest you need more fluid.
Sources & further reading
- EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA) (2010). Scientific Opinion on Dietary Reference Values for water . EFSA Journal 8(3):1459 · doi:10.2903/j.efsa.2010.1459
- American College of Sports Medicine; Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS (2007). American College of Sports Medicine position stand. Exercise and fluid replacement . Med Sci Sports Exerc 39(2):377–390 · doi:10.1249/mss.0b013e31802ca597
- Institute of Medicine (2005). Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate . The National Academies Press · doi:10.17226/10925