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How Much Water Should I Drink a Day?
The real recommendation (not the 8-glasses myth)
The famous "8 glasses a day" (about 1.9 L) is a simplification with no strong scientific basis. The most-cited evidence-based guidance comes from the U.S. National Academies of Sciences, Engineering, and Medicine, which sets adequate intake at 3.7 L/day of total water for men and 2.7 L/day for women — including the ~20% you get from food. The UK NHS suggests 6–8 cups of fluid daily as a floor, and the European Food Safety Authority recommends 2.0 L for women and 2.5 L for men.
The honest answer, though, is that there is no single number. Your daily water needs depend on four main factors:
- Body weight — larger bodies need more fluid. A common estimate is 30–35 ml per kg of body weight (about 0.5 oz per lb).
- Activity level — you can lose 0.5–2 L per hour of exercise through sweat.
- Climate — heat and humidity increase fluid loss significantly, as does high altitude.
- Life stage and health — pregnancy, breastfeeding, fever, and some medications all raise your needs.
Daily water intake by body weight
| Body weight | Estimated daily drinking goal* | In ounces |
|---|---|---|
| 50 kg (110 lb) | 1.5–1.75 L | 51–59 oz |
| 60 kg (132 lb) | 1.8–2.1 L | 61–71 oz |
| 70 kg (154 lb) | 2.1–2.45 L | 71–83 oz |
| 80 kg (176 lb) | 2.4–2.8 L | 81–95 oz |
| 90 kg (198 lb) | 2.7–3.15 L | 91–107 oz |
| 100 kg (220 lb) | 3.0–3.5 L | 101–118 oz |
*Using 30–35 ml/kg, before adding extra for exercise (roughly +500–750 ml per 30–60 minutes of sweaty activity) or hot weather. See our water intake calculator guide for the full formula.
Not all fluids hydrate equally
Here's what most advice misses: what you drink matters, not just how much. Peer-reviewed research published in the American Journal of Clinical Nutrition (Maughan et al., 2016) measured the Beverage Hydration Index (BHI) — how much fluid your body actually retains from different drinks compared with still water:
- Still water = 1.0 (baseline)
- Oral rehydration / electrolyte drinks ≈ 1.1
- Sports drinks ≈ 1.05
- Coffee and tea ≈ 0.85–0.95 (mild diuretic effect)
So if your day includes three coffees and a sports drink, your effective hydration is different from the raw milliliters you drank. This is exactly the problem SupaHydrate was built to solve.
How to hit your daily water goal with SupaHydrate
- Get your personalized target. During onboarding, the app calculates your daily goal from your body weight, activity level, and climate — no generic numbers.
- Log every drink in one tap. Water, coffee, tea, juice, electrolytes — each is weighted by its Beverage Hydration Index, so your progress ring shows true hydration.
- Let smart reminders pace you. Notifications adapt to your schedule and back off when you're on track.
- Watch the habit compound. Streaks, weekly averages, and Apple Health sync keep you consistent long after motivation fades.
Can you drink too much water?
Yes, though it's rare. Drinking far beyond your needs in a short window can dilute blood sodium (hyponatremia). A sensible pace is no more than about 1 liter per hour, spread evenly across the day — another reason paced reminders beat chugging to catch up.