1. Why hydration matters
Water is roughly 60% of your body weight. It's the medium for every cellular process you have — temperature regulation, joint lubrication, nutrient transport, blood-volume maintenance, waste removal. A drop of just 2% of body weight in fluid impairs cognitive performance, mood, and aerobic exercise capacity in healthy adults Armstrong 2012. At 4–5%, you start losing measurable strength, accuracy, and judgment — the latter explains why heat-related deaths spike in unusually hot weather.
2. How much water do you actually need?
The U.S. Institute of Medicine sets total water adequate intake at 3.7 L/day for men and 2.7 L/day for women IOM 2005. But — and this matters — about 20% of total water intake comes from food (fruit, vegetables, soup, even bread). So drinking water targets are smaller than people think.
| Group | Total water (food + drink) | Approx. drinking water |
|---|---|---|
| Adult women | 2.7 L | ~2.2 L (≈9 cups) |
| Adult men | 3.7 L | ~3.0 L (≈12 cups) |
| Pregnant women | 3.0 L | ~2.4 L (≈10 cups) |
| Breastfeeding women | 3.8 L | ~3.1 L (≈13 cups) |
| Hot weather / training | +0.5 – 1 L | + 2–4 cups |
The simplest practical method? Drink to thirst, monitor urine colour — both are reliable indicators in healthy adults Armstrong 1998. Aim for the colour of pale lemonade. Anything darker than that = drink more.
Pale yellow = well-hydrated. Dark yellow / amber = under-hydrated. Brown / cola = seek medical advice.
3. Electrolytes — beyond just sodium
Electrolytes are minerals that carry electrical charge in body fluids. The big four for exercise are sodium, potassium, magnesium, and chloride. They control nerve conduction, muscle contraction, and fluid balance across cell membranes.
You lose electrolytes — primarily sodium — in sweat. The American College of Sports Medicine notes typical sweat sodium loss of 500–1,500 mg per litre of sweat, with high variation by individual ACSM 2007. For most one-hour Beachside classes in a normal climate, water alone is fine. For long, hot, or salty-sweater training, supplementing electrolytes prevents the cramping and lightheadedness of hyponatremia (low blood sodium).
When to add electrolytes
- Training >60 minutes in heat
- Heavy sweater (visible salt streaks on shirts)
- Hyrox training, long Saturday sessions
- Water-only fasting + workout
- Recovery from gastrointestinal illness
Practical sources: a pinch of sea salt + lemon in your water bottle, an electrolyte tab, coconut water for moderate sodium, or a balanced sports drink for long efforts.
4. Hydration around exercise
The ACSM and the Academy of Nutrition and Dietetics joint position stand Thomas 2016 recommends:
- 2–4 hours before training: 5–10 mL/kg of fluid (~350–700 mL for a 70 kg adult).
- During training of >60 min: 0.4–0.8 L/hour, with electrolytes if intense or hot.
- After training: replace 125–150% of fluid lost. Weigh yourself before and after — every 1 kg lost = ~1.25–1.5 L to drink back over the next several hours.
For Wasaga summer outdoor sessions, plan ahead. Heat illness is preventable but kills people every year — usually in the first hot week of the season before the body has acclimated Casa 2015.
5. Signs of dehydration
- Mild (1–2% body weight loss): thirst, slightly dry mouth, urine darkening, mild headache.
- Moderate (3–5%): noticeable strength drop, dizziness on standing, irritability, muscle cramping, reduced sweating.
- Severe (>5%): rapid heart rate, confusion, very dark urine or oliguria, fainting. Medical emergency.
Older adults are at particular risk because the thirst response weakens with age Stookey 2005. If you're 65+, drink to a schedule, not to thirst.
6. Caffeine and alcohol
The folk belief that coffee dehydrates you is largely a myth. Habitual coffee drinkers show no net dehydrating effect from moderate intake (up to ~400 mg/day, about 4 cups) — caffeine is a mild diuretic, but the water in the coffee more than compensates Killer 2014.
Alcohol is different. It's a true diuretic, and a single bout of moderate-to-heavy drinking causes a measurable next-day fluid deficit on top of disrupted sleep and impaired muscle protein synthesis. If you drink, alternate with water and add electrolytes.
7. Common myths
"You need 8 glasses of water a day."
The truth: The "8×8" rule has no peer-reviewed origin. Actual fluid needs vary widely by body size, food intake, and activity. Use thirst + urine colour, not a rigid count Valtin 2002.
"If you're thirsty, you're already dehydrated."
The truth: Thirst typically kicks in at ~1% fluid loss — well before any meaningful performance impact. It's a reliable signal in most healthy adults, not a panic alarm.
"Sports drinks are always better than water."
The truth: For sub-60-min training, plain water is fine and the sugar in sports drinks is unnecessary calories. They earn their place during long, hot, or repeated-bout efforts.