Search "hydration summer exercise" and you'll find a hundred opinions, a few hundred ads and one very expensive electrolyte tin. Here's the calm version, built for people training in Toronto's heat and humidity.
Toronto summers are no joke. It gets sticky by June, sweaty by July, and downright soupy when a humidex warning rolls in. Your body copes, but it needs help from you. Let's keep this simple.
Hydration summer exercise basics: start hydrated, sip steadily, replace what you lose
Health Canada's guidance on protecting yourself from extreme heat is clear: drink water before you feel thirsty, since you can be dehydrated without feeling thirsty. Drink before, during and after physical activity. It also suggests eating water-rich foods like fruits and vegetables.
That's the foundation. No special formula, no complicated math. Start the day well, drink around your workout, and top up afterwards.
How do you know if you're drinking enough?
Use your own body as the gauge.
- Urine colour. Pale yellow, like light lemonade, is usually fine. Dark yellow can mean you need more fluid. Health Canada lists dark yellow urine among the signs of heat exhaustion.
- Thirst. Don't ignore it, but don't wait for it either.
- Energy and headache. A low-grade headache and a flat workout can be an early hint you're running dry.
- The weigh-in test. If you're curious, weigh yourself (lightly dressed) before and after a hard session. The difference gives you a rough idea of what you lost in sweat, and that's what to replace over the next few hours. A one kilogram drop is roughly a litre of fluid.
Don't overdo it either
You can drink too much. Chugging far more than you're sweating out, especially over a long session, can dilute your blood sodium, and that's dangerous. For a typical gym class or a run under an hour, you don't need to force fluids. Sip to stay comfortable, and eat normally.
If you're training long, in serious heat, or you're a heavy sweater who notices white salt marks on your clothes, adding some sodium to your fluids or food makes sense. A salty snack does the job for most people.
Training in the heat: a few smart habits
Health Canada's tips for being active in the heat are practical:
- Plan the hard stuff for cooler times of day. Early mornings and evenings beat 2 p.m.
- Ease in early in the season. Your body isn't used to heat yet, so start gradually.
- Take extra breaks, and don't expect your usual performance. Heat slows everyone down. It's not you.
- Dress for it. Light, breathable clothes. Hats and sunscreen outside.
Late May is the perfect time to adjust. A run that felt easy in April can feel brutal when the humidity jumps. Turn the dial down for a couple of weeks and let your body adapt.
What to drink, and what to skip
Water is the default, and it's enough for most workouts. Milk, a bit of juice, coconut water and a salty snack all count toward what you're replacing after a tough session. Sports drinks have a job, but it's mostly for long, hard efforts when you also need carbohydrates and sodium, not for a 45-minute class.
Coffee counts toward your fluids too. Most people tolerate their usual amount just fine. What's worth watching is alcohol the night before a hot-weather session: it tends to leave you dry and flat. Not a lecture, just a heads up from someone who's coached a lot of sweaty Saturday mornings.
Know the warning signs
Heat exhaustion can show up as headache, nausea, dizziness, rapid heartbeat, extreme thirst and dark urine. If that happens, stop, move somewhere cool and drink water right away.
Heat stroke is a medical emergency. Warning signs include confusion, a high body temperature, poor coordination and hot, red skin. Health Canada says to call 911 immediately if you see them. While you wait, cool the person down with fans and cold water on large areas of skin or clothing.
If you have a heart condition, take medication that affects hydration, or have any health concerns, talk to your doctor about exercising in the heat.
What this looks like at the gym
Our spaces are built for people who train in all seasons. If you're in a small group class, your coach will build in water breaks and scale the work on hot days, and we'd rather you take a break than push through feeling dizzy. At open gym, you set your own pace, so bring a bottle and listen to your body.
For more on fuelling and eating around training, take a look at our nutrition page. And if you're planning a summer race, our HYROX and DEKA training includes plenty of conditioning, so hydration planning is worth practising before the event.
A simple day-of plan
Here's what it can look like on a training day. Drink a glass or two of water with breakfast. Sip steadily through the morning. Have a glass about an hour before you train. Sip during the session as you need to. Afterwards, drink with your meal and keep an eye on that urine colour for the rest of the day. That's it. No timers, no apps, no powders unless you want them.
Quick answers
How much water should I drink when I exercise in summer?
There's no single number. Drink before, during and after activity, sip steadily, and use pale yellow urine as a rough guide. Drink more on hot, humid days.
Do I need electrolytes for a one-hour workout?
Usually not. Water and a normal meal are enough for most people. Long sessions or heavy sweating may call for added sodium.
Can you drink too much water?
Yes. Drinking far more than you sweat can dilute blood sodium. Sip to comfort rather than forcing fluids.
What are the signs of dehydration during exercise?
Extreme thirst, dark yellow urine, headache, dizziness and fatigue. If you feel unwell, stop, cool down and drink water.
Train smart this summer
Tour a Stay Gold gym and get coached through the hot months.