Hydration and Electrolytes: How Much Water You Need and How to Drink Around Training

Losing just 2% of your body weight in water can noticeably lower focus and exercise performance. To get the most out of training, hydration is a foundation as important as nutrition. This guide covers how much water you need per day, the role of the electrolytes you lose in sweat, and how to hydrate before, during and after a workout.

Why hydration matters

Your body is roughly 60% water. Water regulates temperature (cooling you through sweat), transports nutrients and oxygen, and lubricates joints. During exercise you lose water as sweat, and as dehydration builds it shows up like this:

• About 2% dehydration: reduced endurance and focus, exercise feels harder.
• About 3–5% dehydration: lower strength and power, rising body temperature, higher heat-illness risk.

In other words, "drink once you're thirsty" is sometimes too late — it helps to sip steadily before thirst sets in.

How much water you need per day

Daily needs vary by individual, but a common rule of thumb for fluids is 30–40 mL per kg of body weight (water in food is separate). Start here, then adjust for season and activity.

This is a baseline for ordinary days; on training days you add sweat losses on top. To get your own target from weight, age, sex and activity, use the Water Intake Calculator.

What are electrolytes? The minerals you lose in sweat

Electrolytes are minerals that carry an electric charge when dissolved in water (sodium, potassium, magnesium and others). They regulate your fluid balance and nerve and muscle function, and they are lost in sweat. Drinking only large amounts of plain water can dilute blood electrolytes and, ironically, cause problems such as cramps or headaches.

For exercise under an hour, plain water is usually enough. For sessions over an hour or heavy sweating, a sodium-containing sports drink or oral rehydration solution helps. Getting a good mineral balance from everyday meals is the foundation of electrolyte replacement.

Hydration before, during and after training

Knowing "when and how much" for each phase makes it easy to put into practice. The figures below are general guides.

• Before (2–3 hours prior): about 2 cups (~400–600 mL), sipped gradually. Don't chug right before starting.
• During: a sip to half a cup (~150–250 mL) every 15–20 minutes. Use a sodium drink for long or high-intensity sessions.
• After: replace based on weight lost. Aim for 1–1.5× the amount lost, restored slowly over a few hours.

Overhydration and other cautions

• Don't drink huge amounts of water in a short time: rarely this causes hyponatremia (water intoxication). For long sessions, take electrolytes, not just water.
• Don't rely on caffeine or alcohol: they have a diuretic effect and aren't reliable for hydration (see the caffeine intake guide).
• Thirst is already an early sign of dehydration: sip before it hits.
• If you have a medical condition: anyone on fluid or salt restriction (heart or kidney disease, etc.) should follow their doctor, not increase intake on their own.

Summary

Think of hydration as "baseline + sweat losses." Use weight × 30–40 mL for your baseline, then add what the before/after weight difference shows you lost on training days. For sessions over an hour or heavy sweating, replace electrolytes such as sodium along with fluid. Start by checking your daily target with the Water Intake Calculator.