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Hydration is one of the most important aspects of running performance, yet it can also be one of the most confusing. We know we need to drink enough, particularly during longer runs and when running in hot weather, but how much fluid do we actually need? Can you drink too much? And is water always the best choice, or are sports drinks sometimes worth considering?

The truth is that hydration needs vary from runner to runner, depending on factors such as pace, distance, weather conditions and how much you sweat. Understanding the basics can help you avoid dehydration, perform at your best and recover more effectively. Here’s everything you need to know about staying properly hydrated before, during and after your runs.

Why do we need to hydrate when we run?

Being more than two per cent dehydrated causes a decline in performance. When you run, water and electrolytes (calcium, potassium, magnesium and sodium) are lost when you sweat.

“Hydration isn’t just about water, especially in summer conditions. Sweat loss impacts everything from muscle contractions to decision-making,” explains Dr. Samuel Impey, performance nutritionist and Puresport scientific advisor.

How much we sweat is influenced by a range of factors, such as weather, individual sweat rates, running intensity and efficiency, on average runners can expect average sweat rates of 1 to 2.5 litres per hour.

Dehydration causes your blood volume to drop, which lowers your body’s ability to transfer heat and forces your heart to beat faster, making it difficult for your body to meet aerobic demands – and running feel harder.

Monitoring your hydration levels

To perform at your best, it’s recommended that you start a run in a hydrated state and stay less than two per cent dehydrated. One of the easiest ways to monitor your hydration status is by weighing yourself before and after long runs to see how much water weight you’ve lost as sweat.

Another way is to pay attention to the colour and frequency of your urine. It should be a pale straw or pale yellow colour.

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How much do I need to drink to hydrate?

To determine your own hydration needs, it is important to listen to your own body as quantities will vary, but here are some general guidelines.

Pre-run hydration

Ideally, aim to drink 400-500ml one to two hours before a run. If you’re short of time or run first thing in the morning, then try to consume 100-200ml 15 to 30 minutes before going out.

Hydrate during your runs

This will depend on how long your run is and what the weather is like. On short runs, you probably don’t need to take a drink with you, but some runners feel more comfortable having one to hand.

For longer runs you may need to take a water bottle or hydration vest with you. Aim to drink 100-200ml every 20 minutes.

One of the easiest ways is to set your watch to beep every 15 to 20 minutes to remind you to take a drink. Drinking smaller amounts at regular intervals can help you absorb fluid more effectively without a stomach upset.

How to hydrate after your run

If you want to measure how much fluid you’ve lost as sweat, you can weight yourself before and after your run to see the difference. Aim to drink around one litre of hypotonic or isotonic drink for every 1kg total weight loss. Look for a drink that contains around 50 mmol sodium per litre, as well as potassium and magnesium.

Remember that after your run you should also be looking to refuel with a good mix of carbs and protein, so a recovery smoothie can form part of your rehydration plan too.

What are electrolyte drinks?

Electrolyte drinks are fluids that contain key minerals such as sodium, potassium, magnesium and calcium and are designed to help replace what you lose through sweat during exercise. They help maintain fluid balance, support muscle function and prevent dehydration-related issues like cramps or fatigue.

These drinks come in many forms, from ready-made sports drinks to tablets, powders or DIY mixes you can add to water. Some are formulated with added carbohydrates for energy, while others focus purely on hydration with minimal sugar. The right option depends on your workout length, intensity and personal preferences.

Do I need an electrolyte drink?

For most short runs under an hour, plain water is usually enough to keep you hydrated. However, if you’re running for longer, training in hot weather, or sweating heavily, an electrolyte drink can help replace the minerals lost through sweat and support your performance.

Signs that you might benefit from one include feeling fatigued, getting muscle cramps, or noticing salt on your skin or clothes after a run.

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Are you drinking too much?

Over hydrating can actually be more dangerous than not drinking enough. Hyponatremia occurs when your fluid intake exceeds your rate of fluid loss from sweating, which results in low blood-sodium levels and it can be fatal.

Symptoms of hyponatremia include:

• Nausea.
• Disorientation.
• Muscle weakness.

Hyponatremia can develop in faster runners who are sweating out sodium at such a rapid rate that water or sports drink are not adequately replacing it. It can also occur in runners who are drinking more fluid than they are sweating, thereby diluting their blood sodium. This tends to be more of a problem for slower runners during long runs or races where they may stop at every water station but not necessarily needing or using the amount of fluid they are drinking.

How to avoid hyponatremia

You can avoid the risk of hyponatremia by monitoring your fluid intake before, during and after runs (see below) and making use of electrolyte drinks which contain sodium and potassium, or adding hydration sports sachets to your water bottle. As a general guideline, in hot weather if you are running longer than 30 minutes, choose a sports drink that includes electrolytes.

One of the best guides to maintaining an optimal hydration state is actually thirst! The concept of drinking according to thirst may seem too simple to be an accurate barometer of fluid needs. However, there is now increasing scientific evidence to support the notion that thirst is actually the ideal way to gauge hydration needs. So if you don’t feel thirsty, you can probably skip the water station.

Too hot to run outside? Check out our treadmill workouts.