“8 glasses a day” is catchy—but your ideal water intake actually depends on your body size, activity, climate, diet, and health status. This guide gives you an answer-first framework with simple formulas, smart tables (US + metric), workout adjustments, signs of under/overhydration, and easy routines. We’ve also linked tools and references so you can personalize your plan—without falling for myths.

What “Counts” Toward Daily Water?

Hydration isn’t just plain water. Your daily total includes water + unsweetened tea/coffee + sparkling water + soups + high-water foods (fruits/vegetables). Alcohol and very sugary drinks don’t help much—they can be dehydrating or add empty calories.

Simple Baseline Formulas (Pick One)

• Metric: 30–35 ml × body weight (kg) → daily ml goal. Example: 70 kg → 2.1–2.45 L/day.
• US: 0.5–1.0 fl oz × body weight (lb) → daily ounces. Example: 160 lb → 80–160 fl oz (2.4–4.7 L). Most people feel best nearer the middle.
• Easy default: ~2–3 L/day for many adults, then adjust for sweat, heat, and thirst cues.

These are starting points, not medical prescriptions. Hydration needs vary day to day—listen to your body and the environment.

Quick Targets by Body Weight

Exercise & Hot Weather: How Much Extra?

• Before workouts: Drink ~300–500 ml during the hour before exercise.
• During workouts: Aim for about 350–500 ml per 30 minutes of vigorous exercise (more if you sweat heavily).
• After workouts: If you can, weigh yourself pre/post. For each 0.5 kg lost, replace with ~500–700 ml fluid plus electrolytes.
• Electrolytes: For long, sweaty sessions or heat, include sodium + potassium. For easy/short sessions, water is usually enough.

Simple Signs You’re Hitting the Mark

How to Hit Your Target (Without Thinking All Day)

1. Choose a bottle you’ll carry: 500–750 ml sizes are easy at work and in transit.
2. Micro-goals: Example for a 2.4 L target—1 bottle by 10am, 1 by 1pm, 1 by 4pm, 1 by 7pm.
3. Flavor, not sugar: Lemon, cucumber, mint; or plain sparkling water with a citrus twist (then rinse with still water to protect teeth).
4. Front-load earlier: More in the daytime; taper after dinner to protect sleep.
5. Use a tracker: Mark lines on your bottle—or try our calculator below.

Related Guides & Tools

• What Is Still Water?
• Is Sparkling Water Good for You?
• Is Lemon Water Good for You?
• Daily Water Intake Calculator

FAQs

Is “8×8” (eight 8-oz glasses) enough?

It’s a simple rule but not personalized. Use 30–35 ml/kg or 0.5–1.0 fl oz/lb and adjust for heat and activity.

Do tea and coffee count?

Yes—unsweetened tea/coffee contribute to hydration. Very caffeinated or sugary drinks aren’t ideal base fluids.

How much should I drink during workouts?

Roughly 350–500 ml per 30 minutes of vigorous exercise. Add electrolytes for long/hot sessions.

Can you drink too much water?

Yes—rarely, but possible. Don’t force extreme intakes; include electrolytes with heavy sweat; listen to thirst and comfort.

Any special cases?

Pregnancy/breastfeeding, kidney/heart issues, or medications may change needs. Get individualized guidance from your clinician.

References

• CDC — Water & Healthier Drinks
• Harvard Health — Hydration & Health
• NIDDK — Dehydration
• American Dental Association — Dental Erosion (for acidic beverages)

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