Hydration in Training: How Much Water, Electrolytes and Signs of Dehydration

Hydration is the most underrated detail of training. A 2% drop in body weight due to dehydration already reduces performance by 10 to 20% in various sports. This article shows you how to get your water right and when electrolytes are helpful.

How much to drink per day

Direct answer: Between 35 and 45 ml per kg of body weight per day for a moderate athlete. In heat, high training volume or high sweating, it increases to 50 to 60 ml/kg. Includes water, teas, coffee, fruits and liquid foods.

Practical examples:

Weight	Base volume	On a hot day
60 kg	2,1 a 2,7 L	3,0 a 3,6 L
70 kg	2,5 a 3,2 L	3,5 a 4,2 L
80 kg	2,8 a 3,6 L	4,0 a 4,8 L
90 kg	3,2 a 4,1 L	4,5 a 5,4 L

Hydration around training

Pre-workout

• 400 to 600 ml 2 to 3 hours before
• Supplement with 200 to 300 ml, 15 minutes before

During training

• Training <60 min: 150 to 250 ml every 15–20 min
• Training >60 min intense: 500 to 750 ml/h + electrolytes
• Monitor individual sweating

Post-workout

• Weigh before and after: 0.5 kg lost = 500 to 750 ml to replace
• In the next 2 to 4 hours, complete replacement

Electrolytes: When They Matter

Main lost in sweat

• Sodium (Na+): main; varies greatly between individuals (200 to 2000 mg/L of sweat)
• Potassium (K+): moderate
• Magnesium (Mg): small
• Chloride (Cl−): accompanies sodium

When electrolytes make a difference

• Workouts >60–90 min at high intensity
• Heat and high sweating
• “Salty” sweating (white mark on clothes after drying)
• Recurrent cramps
• Long run, trail, football, sports in hot season

How to supplement

• Commercial isotonic drinks: practical but with a lot of sugar
• Electrolyte tablets in water
• Homemade mix: 500 ml of water + 1 pinch of salt + lemon juice + 1 spoon of honey

Signs of dehydration

Level	Signs
Light (2% weight)	Thirst, yellowish urine, slight loss of focus
Moderate (3–5%)	Headache, fatigue, cramps, dry mouth
Severe (>5%)	Dizziness, confusion, tachycardia, sweating stop

Performance already drops in the light phase. Do not expect extreme thirst.

urine scale

• Very light/transparent yellow: well hydrated (may even be too much)
• Light to medium yellow: suitable
• Dark yellow: starting to dehydrate
• Orange or brown: major dehydration (or rhabdomyolysis; seek help)

Myths

“8 glasses a day for everyone.” Simplification. It varies with weight, climate, training, diet.

“If you’re thirsty, you’re already dehydrated.” Partially true; Thirst is a late sign in some, but it is not a catastrophic failure. Proactively hydrate on training days.

“Coffee dehydrates.” Diuretic effect is small in habitual users. Coffee contributes to total liquids.

“Water with lemon speeds up metabolism.” Myth. Just hydrates.

“Beer after training replenishes.” Alcohol is a diuretic and disrupts protein synthesis. Avoid or moderate post-workout.

Common mistakes

Drinking everything at once during training. Generates discomfort; prefer frequent sips.

Forget water during short intense training. Even 45 minutes intense in summer already loses 500 to 1000 ml.

Use isotonic in a 30-minute workout. Unnecessary extra calories.

Neglecting post-workout. Many people forget to replenish in the next 2 to 4 hours.

Drink too much water before bed. Interrupts sleep with trips to the bathroom; adjust to before 8pm.

Tips used by personal trainers

• Student arrives with a headache or “no strength”: check water and sleep before anything else
• 750 ml bottle at the gym is a visual reminder to keep pace
• Student with recurrent cramps: check dietary sodium and total water before supplementing magnesium
• Post-workout, 500 ml of water + protein accelerates the feeling of recovery
• In short, drinking more water helps satiety and reduces confusion between hunger and thirst

Key Points

• 35 to 45 ml/kg/day base; more in heat and high training
• 500 ml before, 150–250 ml every 15 min during, replace 100–150% of weight lost after
• Water is sufficient for most workouts; electrolytes in long sessions and heat
• Mild signs (dark urine, thirst, headache) already mean a drop in performance
• Avoid excess; It’s not a race for “higher intake”

---

Additional reading:

• Pre and post-workout meal
• Pre-workout: ingredients that work
• Pre-workout caffeine: dose
• TDEE and energy expenditure