Why one rule does not fit everyone
Sweat rates vary enormously, from less than half a litre to more than two litres per hour, depending on the person, the intensity and the conditions. That is why fixed advice, like a set number of cups per hour, often misses the mark.
Losing a lot of fluid makes hard efforts feel harder and can hurt performance, especially in the heat. Drinking more than you lose is also a problem: it can dilute the sodium in your blood (hyponatremia), which can be dangerous. The aim is a personal plan between those two extremes, and it changes with the season. A humid summer race, an indoor arena and a winter ski outing are three different situations.
Calculate your sweat rate
Weigh yourself before and after a typical session, in minimal clothing and towel-dried, and note what you drank. Each kilogram lost is about one litre of sweat.
Session length
Repeat in different conditions: sweat rates change with heat, intensity and season. Bathroom breaks during the session make the estimate a little high.
Your sweat rate, about
1.3L per hour
In similar sessions, you can drink up to 1.3 L per hour. Your losses stayed under 2%.
- Body weight lost
- 0.8 kg (1.1%)
- To drink afterwards
- 1–1.2 L
Water, sports drink or electrolytes?
They do different jobs. Pick by session length and conditions, not by marketing.
| Option | What it gives you | Best for |
|---|---|---|
| Water | Fluid only | Most sessions under an hour |
| Sports drink | Fluid, carbohydrate (about 6%) and some sodium | Long or hard sessions, when you need fuel and fluid together |
| Electrolyte tablets or powders | Fluid and sodium, usually little or no carbohydrate | Long or hot sessions when fuel comes from food, or for salty sweaters |
| Oral rehydration solution | Sodium with a little sugar, designed for rehydration | After heavy losses or illness; not a performance drink |
| Salty foods with water | Sodium from food: pretzels, broth, salted potatoes | All-day and ultra events, and meals after training |
Heat, cold and indoor arenas
The same session can call for a very different drinking plan depending on where you train.
- Hot and humid days
Sweat rates climb
Start well hydrated, drink regularly, and add sodium in sessions over an hour. Your body adapts to heat over 1 to 2 weeks.
- Cold drinks before and during
- Train early or late
- Salty snacks after
- Cold weather
Thirst is weaker
You still sweat under layers, and cold, dry air adds to fluid losses. Plan to drink even if you are not thirsty.
- Insulated bottle
- Warm drinks
- Weigh before and after a long outing
- Indoor arenas and gyms
Gear traps heat
Hockey and other equipment-heavy sports can produce large sweat losses, even on a cold rink.
- Bottle on the bench
- Weigh before and after a game
- Sports drink for long practices
How much to drink, and when
Start hydrated
Drinking about 5 to 7 mL per kg of body weight around 4 hours before a long or hot session lets your body absorb what it needs and pass the rest.
During exercise
If you have not measured your sweat rate, about 0.4 to 0.8 L per hour is a reasonable starting point, adjusted for heat, intensity and body size. Small, regular sips are easier than large amounts at once.
Limit losses, do not overshoot
For most sessions, a sensible goal is to keep losses under about 2% of body weight. Gaining weight during exercise means you drank too much.
When sodium helps
In long sessions, in the heat, or if you are a salty sweater (white marks on your clothes), sodium helps you hold on to fluid. Sports drinks usually contain about 450 to 700 mg per litre; losses vary widely from person to person.
Rehydrate after
Over the following hours, drink roughly 125 to 150% of the fluid you lost, with meals or salty snacks.
A quick check
Pale yellow urine is a rough sign you are well hydrated. Dark urine, a headache or unusual fatigue after training can mean you are falling short.
WORKING WITH YOUR DIETITIAN
How we work on it together
Measure in real conditions
We go through your sweat-rate numbers across hot and cool sessions, and look for patterns such as heavy or salty sweating.
Write your drinking plan
What to drink, how much and when, before, during and after training and events, with summer and winter adjustments.
Combine it with your fueling
Fluid, sodium and carbohydrate work together, so your hydration plan fits the rest of your training and race-day nutrition.
Common questions
How much should I drink per hour during exercise?
It depends on your sweat rate. Without a measurement, about 0.4 to 0.8 L per hour is a reasonable starting point. Measuring your sweat rate lets you narrow it down, so you limit losses to about 2% of body weight without drinking more than you lose.
Water, sports drink or electrolyte tablets: which is best?
Water is enough for most sessions under an hour. Sports drinks add carbohydrate and sodium for long or hard sessions. Electrolyte tablets add sodium without much fuel, which suits long or hot sessions when you eat for energy, or heavy salty sweaters.
Can you drink too much water during exercise?
Yes. Drinking more than you sweat during long events can dilute the sodium in your blood (hyponatremia), which can be dangerous. Gaining weight during exercise is the warning sign. Drink to a plan based on your sweat rate, not at every opportunity.
Does coffee dehydrate you?
Not in usual amounts. For people who drink coffee regularly, moderate amounts count toward fluid intake. Very large doses of caffeine can slightly increase urine output.
Do I need electrolyte drinks every time I train?
No. For most sessions under an hour, water is enough. Electrolytes are most useful in long sessions, hot or humid conditions, and for heavy or salty sweaters.
Are muscle cramps caused by dehydration?
Sometimes, but not always. Cramps are also linked to fatigue and muscle overload. Fluid and sodium help some athletes, so the cause is worth looking at individually.
How much water should I drink in a day?
It depends on your size, activity and climate. Most athletes do well drinking with meals and snacks, responding to thirst, and adding a specific plan around training.
Based on current sports nutrition guidelines
- Thomas, Erdman & Burke (2016). Nutrition and Athletic Performance. ACSM, Academy of Nutrition and Dietetics & Dietitians of Canada joint position statement.
- Sawka et al. (2007). ACSM position stand: exercise and fluid replacement.
- Hew-Butler et al. (2015). Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference. British Journal of Sports Medicine.
This page is general information, not individual advice. Your needs depend on your sport, health and goals.
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