Runner drinking water on a hot day

Running plans & training

How much do you really need to drink during long, hot runs? Practical advice on water, salts and timing.

More nutrition & recovery

01 · Why hydration is crucialWhy hydration is crucial

Before the run

Start hydrated so heart rate and effort stay more stable.

During the run

Drink regularly and add electrolytes when heat or duration demands it.

After the run

Replace fluid loss and cool down actively to recover faster.

Running in the heat increases the burden on your heart, muscles and nervous system. Your body tries to cool down by sweating more — sometimes as much as 1 to 2 liters per hour, depending on heat, intensity and your individual sweating pattern. That sweat consists not only of water, but also of important electrolytes such as sodium, potassium and magnesium. If you do not replenish this in time, your heart rate will increase faster, your pace will feel heavier and the risk of dehydration, cramps and overheating increases.

Hydration is therefore not just about “drinking enough”, but about the right timing, right amounts and right composition. What, how much and when you drink determines how much your body can cool and how efficiently you use energy. Smart hydration means you maintain your performance, speed up your recovery and run much safer — especially on long runs or training in the sun.

Hydration also works best with a good nutrition plan. A correct balance between carbohydrates, fluid and salt ensures that your heart rate remains stable and your energy reserves last longer. Also check out What to eat before a run? for ideas on how to plan carbs and salt hand in hand so your body can perform optimally in warm conditions.

02 · Before the runBefore the run

Heat requires preparation. Your body must have enough fluid and electrolytes before you start running, otherwise you will already be behind. In warm conditions, good pre-run hydration can make the difference between a steady workout and heavy decline after a few km.

Drink 5–7 ml of water per kilo of body weight in the three hours beforehand.
Example: at 70 kg = 350–490 ml spread over a few moments.
Add 300–500 mg sodium via a sports drink or ORS to help you retain fluid more effectively — especially important if you sweat a lot.
Cool your wrists and neck with a wet towel or cool pack to keep your core temperature low before the start.
Check temperature and humidity; High humidity prevents sweat from evaporating, causing you to overheat more quickly. So adjust your pace in advance.

Are you unsure about supplements? Supplements for runners explains when electrolytes, magnesium or nitrates have added value and when it is better to avoid them.

03 · During the runDuring the run

During hot runs, the emphasis is on constant small sips and replenishing salt to monitor your fluid balance. Avoid waiting until you're thirsty — that's a sign you're already behind.

Take 150–250 ml of fluid every 15–20 minutes, depending on your sweat loss and the temperature.
For workouts longer than 60 minutes: choose an isotonic sports drink (6–8% carbohydrates + electrolytes) to replenish both energy and salt.
Wear light, breathable clothing and use a cap or sun visor to limit direct sunlight and cool your face.
Plan your route smartly: run past water points, fountains or take a drinking belt, vest or handheld bottle with you. The right gear makes a heat run much safer.

Do you want to discover which drinking system suits you best? Read Best Accessories for Runners for options and comparison.

< 45 min. Water is usually sufficient
45–90 min. Water + electrolytes in warm weather
> 90 min. Isotonic sports drink (carbs + electrolytes)

Please note: do you sweat extremely much? Then consider a sodium supplement (electrolyte capsule) for runs > 90 minutes, especially in the sun.

04 · After the runAfter the run

Hydration doesn't stop when you're done — that's when recovery begins. By quickly and specifically replenishing fluids and electrolytes, you lower your heart rate, feel fit faster and reduce the risk of cramps or headaches later in the day.

Weigh yourself before and after running. 1 kg weight loss ≈ 1 liter fluid loss.
Drink back 150% of that difference within 2 hours to fully restore your fluid balance.
Example: 1.5 kg lost → Drink back 2.25 liters over 1–2 hours.
Add electrolytes via sports drink, ORS or a salt capsule to restore your sodium and mineral balance.
Put on dry clothing, keep moving lightly in the first few minutes and cool your wrists, neck and forehead again to normalize your core temperature faster.

Combine your fluid plan with good nutrition for optimal recovery. Read Recovery Food: Best Post-Workout Snacks and Drinks for simple, effective recovery meals and snacks.

05 · Signs of dehydrationSigns of dehydration

Dehydration rarely comes suddenly; it builds up gradually as your body loses more and more fluid and electrolytes. At first, you may just notice that your mouth becomes dry or that your pace feels a little less smooth. But as your core temperature rises and your blood volume drops, your heart has to work harder to maintain the same effort.

Many runners miss these early signals and continue running to the point where performance abruptly collapses: an unexpectedly high heart rate, dizziness, or a sudden heaviness in the legs. By recognizing the subtle warnings and responding immediately — drink, cool, slow down — you stay safe and keep your training effective.

Dark urine or little urination. Your body tries to retain fluid, a classic sign of dehydration.
Dizziness or headache. A drop in blood volume makes your heart work harder — your brain gets less oxygen.
Sudden drop in pace. Your cooling system becomes overloaded, meaning you can no longer lose heat.
Heart rate much higher than normal. A body that is too warm or too dry increases your heart rate to compensate.

06 · Extra cooling tipsExtra cooling tips

Heat is one of the biggest performance inhibitors for many runners — not because you are less fit, but because your body simply has to work harder to stay cool. When your core temperature rises, your heart rate shoots up, every pace feels harder, and your risk of dehydration or overheating increases.

Fortunately, you can significantly reduce that pressure with a few strategic cooling techniques. By making smart use of water, clothing, timing and environment, your body stays within a safe temperature zone for longer. This way you not only maintain your performance, but your run also becomes a lot more comfortable and safer.

Start early in the morning or late in the evening. Temperatures and UV are then much lower, which keeps your heart rate more stable.
Put a few ice cubes or a frozen bottle in your vest. Melting ice provides long-lasting cooling and helps keep your core temperature low.
Wet your cap or headband. Evaporating water acts as natural air conditioning — ideal for low humidity.
Pour water over your neck, arms and wrists. These places cool your blood the fastest.
Walk laps close to home or along fountains. This way you always have access to water and you can stop faster if necessary.

07 · MistakesCommon mistakes

Most problems with hot running are not caused by extreme heat, but by small mistakes that accumulate. Think of drinking too little, starting too late, or not taking electrolytes while you sweat a lot. Individually these things seem harmless, but together they cause your body to overheat more quickly and your performance to plummet.

By recognizing and consciously avoiding these common mistakes, you'll keep your heart rate more stable, slow your core temperature, and keep your body functioning efficiently for longer — just what you need to train safely and confidently in warm weather.

Drinking too much water without electrolytes. This can cause you to dilute sodium too much → risk of hyponatremia: nausea, headache, confusion.
Only drink when you are thirsty. Thirst is a late signal. In heat you want to be ahead, not react.
Do not make route planning. Especially on hot runs, you need access to water — fountains, shade areas, shops.
Only drink water afterwards. Without sodium you retain fluid less well and recovery takes much longer.
Stay dressed too warmly. Dark, non-breathable clothing traps heat and pushes your heart rate up.

With a smart heating plan — hydration, pace adjustment, and cooling techniques — you can continue to train safely and strongly in the summer.

08 · FAQFrequently asked questions