How much water should I drink during a workout?

About 200–300 ml (7–10 oz) every 15–20 minutes of exercise, adjusted upward for heat and heavy sweating, per ACSM guidance.

How much water should I drink after exercising?

Replace 125–150% of the body weight you lost — about 1.25–1.5 liters per kilogram. Weighing yourself before and after a session tells you your personal sweat rate.

Should I drink water or a sports drink at the gym?

For sessions under ~60 minutes, water is sufficient. Beyond an hour, in heat, or with heavy sweat, a sports or electrolyte drink (BHI ≈ 1.05–1.1) replaces sodium and retains fluid better than water alone.

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How Much Water Should You Drink When Working Out?

Quick answer: Drink about 500 ml (17 oz) 2 hours before exercising, 200–300 ml (7–10 oz) every 15–20 minutes during, and afterwards replace 125–150% of the weight you lost (1.25–1.5 L per kg). For sessions under an hour, water is enough; past 60 minutes or in heat, a sports or electrolyte drink retains fluid better.

Before, during, after: the standard protocol

These targets follow American College of Sports Medicine (ACSM) fluid-replacement guidance:

Phase	How much	Notes
2–3 h before	~500 ml (17 oz)	Start topped up; urine should be pale
15 min before	200–250 ml (7–8 oz)	A final glass
During	200–300 ml every 15–20 min	Sip, don't gulp; more in heat
After	1.25–1.5 L per kg of body weight lost	Weigh before/after to know your sweat loss

Sweat rates vary enormously — from 0.5 to over 2 liters per hour depending on intensity, fitness, heat, and humidity. The before/after weigh-in is the gold-standard way to learn your rate: every kilogram lost is a liter of sweat.

Water or sports drink?

Under 60 minutes, moderate intensity: plain water is all you need.
Over 60 minutes, high intensity, or hot conditions: a sports drink (BHI ≈ 1.05) or electrolyte solution (BHI ≈ 1.1) replaces sodium lost in sweat and helps the fluid actually stay in your body — the full comparison is in electrolytes vs water.
Skip: energy drinks (caffeine + sugar ≠ rehydration) and alcohol after training, which actively works against fluid retention.

Signs you're under-hydrating your training

Early fatigue, elevated heart rate at normal paces, cramps, headache after sessions, and dark urine are classic markers — a 2% body-water deficit measurably reduces endurance performance. (Full list: signs of dehydration.)

How athletes use SupaHydrate

Set an activity-adjusted goal. Your baseline is calculated from body weight, activity level, and climate — training days carry a higher target than rest days.
Log from your wrist mid-session. The Apple Watch app logs a bottle in two taps between sets (setup guide), and Siri handles it on the run.
Credit sports drinks accurately. Each drink type is weighted by its Beverage Hydration Index — and its sodium, potassium, sugar, and caffeine are tracked with daily-limit warnings.
Review the pattern. Weekly and monthly charts show whether hard-session days consistently come up short — the usual culprit behind "mystery" bad workouts.

Hydration that keeps up with your trainingActivity-based goals, Apple Watch logging & BHI-weighted sports drinks — free on the App Store.

Rule of thumb to remember

Half a liter before, a few gulps every 15–20 minutes during, and 1.5× your losses after. Under an hour: water. Over an hour or sweating hard: add electrolytes. Track it, because guessing is how deficits compound across a training week.

Sources: American College of Sports Medicine — Exercise and Fluid Replacement position stand; Sawka et al., Medicine & Science in Sports & Exercise (2007); Maughan et al., American Journal of Clinical Nutrition (2016).