How Much Water a Day: Calculation & Drinking Schedule

Time

Amount

Morning

399 ml

Late morning

399 ml

Around lunch

399 ml

Afternoon

399 ml

Around dinner

299 ml

Evening

100 ml

Key Takeaways

Formula: 30-35 ml × kg body weight per day, all beverages + food water included

Exercise: +500-750 ml per hour of training, more in heat; weigh before/after for precision

Best gauge: pale-straw urine (lemonade shade) — dark means drink, fully clear means ease off

Overhydration exists: forcing liters beyond thirst risks hyponatremia — more is not better

Core answer: daily total water ≈ body weight (kg) × 30-40ml. A 60kg adult needs ~1.8-2.4L total (including water in food), or ~1,500-1,700ml of plain drinking water. Add +300-500ml per 30 minutes of exercise. The check: pale-lemon urine means you're on target.

The formula

Total water = weight (kg) × 30-40ml
Plain drinking water ≈ total × 80% (food supplies ~20%)

Weight	Total water	Plain water target
50 kg	1.5-2.0 L	1.2-1.6 L
60 kg	1.8-2.4 L	1.5-1.9 L
70 kg	2.1-2.8 L	1.7-2.2 L
80 kg	2.4-3.2 L	1.9-2.6 L

Recommendations by group

The Chinese Dietary Guidelines recommend plain water: 1,700ml/day for adult men, 1,500ml/day for women (temperate climate, light activity).

Special groups: pregnancy +300ml; breastfeeding +600-800ml; older adults should drink small amounts on a schedule (blunted thirst sense).

Exercise and weather adjustments

Exercise: +300-500ml per 30 min of moderate-high intensity (pre-load 400-500ml two hours before)
Heat/dry air: above 30°C or long hours in air conditioning: +500-800ml
Fever/diarrhea: +500-1,000ml as needed; add electrolytes for diarrhea
Coffee/tea: mildly diuretic but still net-positive — each cup of coffee nets ~80% of its water

A drinking schedule

Time	Suggestion
After waking	200-300ml (replenishes overnight loss)
30 min before meals	200ml each
Work breaks	100-150ml per hour
Around exercise	400ml before / small sips during / replenish after
1 hour before bed	100-200ml (earlier if night trips bother you)

Dehydration and overhydration signals

Dehydration: dark-yellow urine, dry mouth, poor focus, headache, constipation

Overhydration (water intoxication / hyponatremia): chugging >3-4L in a short time — dizziness, nausea, confusion. Post-marathon plain-water-only drinking is the classic high-risk scene.

Common mistakes

"8 glasses a day, mandatory": 8 glasses (~2L) is a rough placeholder. Needs vary widely with weight, activity and climate — the weight formula plus urine color is far more scientific.
"Drink only when thirsty": by the time you feel thirst you're already 1-2% down (and performance has dropped). Older adults feel thirst even less — schedule it.
"Any beverage hydrates": sugary drinks hydrate but add a sugar load; alcohol is diuretic and nets negative. Plain water, light tea and sugar-free sparkling water are the best sources.

Frequently Asked Questions

How much water should I drink per day?

Weight-based: 30-35 ml per kg. 60kg → 1.8-2.1L; 70kg → 2.1-2.5L; 85kg → 2.5-3.0L. This covers ALL fluids and food moisture (food supplies ~20%, so ~1.6-2L as drinks for 70kg). Add for exercise (500-750ml/hr), heat, pregnancy (+300ml) and breastfeeding (+700ml). Thirst plus urine color beats any fixed number.

Is "8 glasses a day" a real rule?

It is a misquote of a 1945 recommendation that explicitly noted most water comes from FOOD. No study supports a universal 8-glasses target — needs vary 2× by body size, diet and climate. Fruits, vegetables, soup, tea and coffee all hydrate (caffeine's diuretic effect is too weak to cancel the fluid). Drink to thirst and pale urine; skip the ritual counting.

How do I hydrate for exercise?

Before: 400-600 ml in the 2 hours pre-workout. During: 150-250 ml every 15-20 minutes for sessions over an hour. After: 125-150% of weight lost (sweat 1kg → drink 1.25-1.5L over the next hours). Over 90 minutes or heavy sweating: add electrolytes — plain water alone dilutes sodium and causes cramps or worse.

What urine color means I am hydrated?

Target: pale straw / light lemonade. Dark yellow or amber: drink now. Completely clear, constantly: you may be overdoing it — ease back. First morning urine is naturally darker (overnight concentration), so judge from midday onward. B vitamins (bright yellow) and beetroot (pink) can confound the reading.

Can you drink too much water?

Yes — hyponatremia: sodium diluted below safe levels, causing nausea, confusion, and in extremes seizures. Risk scenarios: endurance events drinking plain water far beyond sweat loss, and "gallon challenge" internet trends forcing 4-5L rapidly. Healthy kidneys handle ~0.8-1L/hour — spread intake, and let thirst lead during exercise rather than rigid schedules.

Do tea and coffee count toward hydration?

Yes. Caffeine is a mild diuretic only at doses above ~500mg (5+ strong coffees), and habitual drinkers adapt within days — net hydration from tea and coffee is positive. Sugary drinks hydrate but cost calories; alcohol genuinely dehydrates (suppresses ADH). For practical purposes: water, tea, coffee, milk and soup all count; beer does not.