There is no single drinking schedule for exercise, because sweat rates differ several-fold between people. The ACSM’s general principles: start exercise well hydrated, drink enough to avoid losing more than about 2% of body weight, and replace fluids afterwards. For typical recreational workouts, drinking to thirst works well.
Before exercise
The ACSM suggests drinking slowly, starting at least about 4 hours before, roughly 5–7 mL per kilogram of body weight (for a 70 kg person, about 350–490 mL). If urine is dark or scant, a small extra amount about 2 hours before can help. These are starting values, not a prescription.
During exercise
The aim is to limit dehydration, not to “fill in a schedule”. The ACSM notes that losing more than about 2% of body weight in sweat can impair performance, and sweat rates are very individual. A practical test: weigh yourself before and after a workout (without clothes, after wiping off sweat) — each kilogram lost is roughly a litre of fluid deficit.
For recreational workouts many people do well simply drinking to thirst — an approach also recommended by international guidance on exercise-associated hyponatraemia.
After exercise
The ACSM states that replacing losses takes roughly 1.5 L of fluid for each kilogram of body weight lost, best spread over time and taken with a meal containing sodium. If you train again within a few hours, replacing fluids matters more than with a long break.
Intensity, duration and temperature
- a short workout (up to about 45–60 minutes) in moderate temperatures — water to thirst is usually enough,
- long, intense workouts or heat and humidity — you sweat more, so you need more fluid and a plan,
- cool weather still calls for drinking — fluid loss does not disappear with the temperature.
Electrolytes during prolonged activity
During long efforts (an hour or more) and with heavy sweating you lose sodium in sweat. In those situations drinks containing sodium, and often carbohydrate, can help; for a short workout water is perfectly adequate. Choose a drink by testing it in training, not on race day.
Risks of drinking too much
Drinking far beyond your needs, especially during many hours of exertion, can dilute blood sodium (exercise-associated hyponatraemia). Symptoms include nausea, headache, confusion and swelling — a dangerous condition that needs medical help. So avoid “drinking by the clock” on a rigid schedule and drink sensibly, largely to thirst.
Practical examples (illustrative)
- Gym, 45–60 min: a bottle of about 500 mL within reach and a few sips between sets; check how much you actually drink and adjust.
- A 10 km run: drink steadily earlier in the day, sip to thirst on the route, and afterwards replace fluids and have a meal.
- A long run or hot day: plan drink stops and consider a drink with sodium; rehearse the plan in training first.
Logging the water you drink in the WODA app helps you see how much you actually drink on training days and rest days. For general guidance see How to Estimate Your Daily Water Needs, and for the signs of low fluid levels Signs of Dehydration.
Frequently asked questions
Should I drink before I feel thirsty?
Be well hydrated before exercise, but during most recreational workouts drinking to thirst is a sensible strategy. In very long efforts and in heat, plan your drinking earlier.
Do I need sports drinks?
Not for a short workout — water is enough. For an hour or more and with heavy sweating, a drink with sodium can help.
How much water after a run?
It depends on your losses. The ACSM suggests roughly 1.5 L per kilogram of body weight lost, over several hours and together with food.
Sources
- Sawka M.N. et al. — ACSM Position Stand: Exercise and Fluid Replacement (Med Sci Sports Exerc 2007;39(2):377–390)
- Hew-Butler T. et al. — Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference (Clin J Sport Med 2015;25(4):303–320)
- NHS — Water, drinks and hydration
This article is for information only and does not replace advice from a doctor or dietitian. If you are unsure or have worrying symptoms, contact a doctor.