Why hydration matters
The body is ~60% water. Drop 1-2% of body weight in fluid and you'll notice mental and physical performance decline. Drop 3-5% and serious impairment sets in.
Daily fluid needs
General adults:
- Women: ~2.7 L (91 oz) total water from all sources
- Men: ~3.7 L (125 oz) total water from all sources
Athletes and hot-environment workers need more. Track urine color — pale yellow = adequately hydrated, dark yellow = under-hydrated.
During exercise
Light sweating (cool gym, moderate effort): 8-12 oz/hour. Moderate sweating: 16-20 oz/hour. Heavy sweating (hot, intense, >60 min): 20-32 oz/hour, plus electrolytes.
Electrolytes — when they actually matter
Electrolytes (sodium, potassium, chloride, magnesium, calcium) regulate fluid balance, nerve signaling, and muscle contraction.
Water alone is fine for:- Sessions <60 minutes
- Cool environments
- Moderate sweating
- Sessions >60 minutes
- Hot environments / heavy sweating
- Multiple training sessions in one day
- Endurance events
- Pre-existing low blood pressure or salt restriction
Hyponatremia — the over-hydration risk
Drinking massive amounts of plain water during long endurance events without sodium replacement dilutes blood sodium. Symptoms: confusion, headache, nausea, in severe cases seizures and death.
Counter-intuitive but real. Marathon runners have died from hyponatremia more than from dehydration.
Rule of thumb for endurance: don't drink more than you sweat, and include sodium.
Hydration signals
Under-hydration:- Dark urine
- Dry mouth
- Headache
- Reduced sweating
- Fatigue
- Elevated resting HR
- Frequent clear urine
- Bloating
- In severe cases: nausea, confusion
Practical hydration coaching
For most clients:
- 1 glass on waking
- 1 glass with each meal
- 1 bottle (16-20 oz) during training
- More if sweating heavily
What about coffee and tea?
Long-debunked myth that caffeine dehydrates. Coffee and tea contribute to total fluid intake. They have a mild diuretic effect, but net fluid is still positive.
Alcohol IS dehydrating. Counter with water alongside it.
TL;DR
Most adults need 90-125 oz total fluid daily, including from food. Water alone is fine under 60 min of training. Add electrolytes for hot, long, or repeated sessions. Hyponatremia (over-hydration with sodium loss) is a real danger in endurance events. Track urine color.