Swimming Dehydration (What to know)


a water bottle in the pool

Swimming is a wonderful and very healthy activity, providing a full-body workout that is gentle on the joints.

As we glide through the water, however, it’s easy to forget that swimming is a high-energy exercise which gets our heart rate pumping and raises our body temperature. As a result, our bodies in the pool will heat up and will need to be cooled, which results in sweating.

Swimming dehydration occurs when you lose too much fluid through sweating while swimming. This can happen because swimming is a very strenuous activity that causes you to sweat a lot. As you are in the water, you may not realise you are dehydrated.

As we are already wet, we trick our brains into thinking that we are hydrated.

Many swimmers do not realise how much they sweat when swimming. Sweating is a natural body function that cools the body once you reach a temperature threshold, regardless of where you are.

In the water, you will not feel the sweat on your skin, therefore many swimmers (myself included) can forget to drink lots of water and to rehydrate.

In this article, I want to fully explore swimming dehydration and how we can so easily become dehydrated as we swim, including:

  • Why do swimmers get dehydrated?
  • Does swimming in a pool hydrate your body?
  • How much water do I need while I swim?
  • Can chlorine dehydrate you?
  • Do you lose electrolytes when you swim?
  • What are the signs of dehydration?
  • How do you prevent dehydration when swimming?

Why Do Swimmers Get Dehydrated?

Swimming is a strenuous activity that can cause you to sweat a lot. This sweating can cause dehydration if you don’t drink enough water to replace what you lose.

Sweating is a natural body function that helps regulate body temperature.

If your body becomes too hot, your sweat glands will release sweat onto the skin. Some of this sweat will just drip off you, however, some of this sweat will evaporate off, removing heat from your body as it vaporises. [source]

Once your core body temperature is too high, you will start sweating regardless of whether you are in the water.

In the water, you may not realise you are sweating as the pool water is washing away the sweat. If the water is cooler and you are doing light exercise, the rate of sweating will be minimal.

How much you sweat while you swim will depend on factors such as:

1. Swimming Intensity

If you are working hard, your body temperature will rise and you will sweat more.

2. Water Temperature

Cooler pool water will help regulate your body temperature so you will sweat less. This is why competition pools are often a little cooler than body temperature to prevent the swimmers from overheating.

3. Ambient Air Temperature

If the ambient air temperature is warm, your body will find it harder to keep itself cool and will need to sweat more to cool down.

How Much Do Swimmers Sweat?

Swimming on average does not produce as much sweat as other land-based activities such as running, but it is amazing how much we can sweat in the pool without realising it.

Studies investigating how much an elite athlete sweats in the pool show us that an elite swimmer loses an average of 125ml per every kilometre that they swim. [source]

Given that a professional swimmer can swim at a speed of 8km/h, that means they will lose about 1000ml or 1 litre of water per hour.

To put that number in context, it might be helpful to compare how much swimmers sweat to how much runners sweat over the same time.

ActivityTime TrainingSweat Rate
(How Much Fluid Is Lost
Swimming60 Minutes800ml – 1000ml
Running60 Minutes2000ml – 2300ml
General Exercise60 Minutes800ml – 1400ml
This Table Shows How Much Swimmers Sweat

You will sweat more doing land-based exercises compared to swimming, however, you will still sweat a lot while swimming and will need to keep hydrated.

Does Swimming In A Pool Hydrate Your Body?

Swimming in a pool does not hydrate the body. We need to ingest water by drinking it to get water to the vital organs and hydrate our bodies.

The body does not absorb water, therefore, just being in a pool will not hydrate the body.

Our skin is a waterproof layer. We need to drink water to stay hydrated.

How Much Water Do I Need While I Swim?

Swimmers need to drink plenty of fluids before, during and after swimming to prevent dehydration.

We are all different shapes and sizes with different workout routines, so it’s difficult to establish how much water we need to intake to support our swimming lifestyle.

As a general rule, if you are not training, divide your weight (in pounds) by two and that is the number of ounces of fluids you will need to drink. If you are going swimming, drink an additional 16 ounces of fluids up to two hours before you get into the pool.

For example, if you are 150lbs, your baseline water intake is 75 fluid ounces, which converts to 2.2 litres.

In addition, up to two hours before you swim, consume an additional 16 fluid ounces, which converts to 0.47 litres.

The above is a guideline based on the desired average percentage of water in your body. [source]

Sweat Rate Test For Swimmers

We are all different, so it’s helpful to get a customised idea of how much you should drink by calculating how much you sweat during a workout.

There are many sweat test techniques available that will help athletes establish their sweat rate for a customised fluid and sodium intake measurement.

The following is the simplest sweat rate test for swimmers:

  1. Weigh yourself (naked) before going to the pool to work out. Ensure your hair is dry. Ensure this measurement is in kilograms.
  2. Note the weight of any food or liquid consumed before or during the swim workout.
  3. After your swim, dry your hair completely.
  4. Weigh yourself again (naked). Ensure this measurement is in kilograms.
  5. Calculate the weight loss by subtracting your second measurement (step 4) from your first weight measurement (step 1).
  6. This weight loss in kilograms can be used to estimate a rough sweat rate in millilitres using the following guide.

1kg of weight loss = approximately 1 litre of sweat output.

For example, if you have found that you lost 0.2kg of weight during your swim, this means you lost 0.2 litres of water.

Can Chlorine Dehydrate You?

Chlorine is used to disinfect and clean swimming pools. It is an important swimming pool chemical used to keep the water clean and kill bacteria.

At present, I cannot find any relevant academic studies which suggest that swimming in chlorine dehydrates a swimmer. [source]

Chlorine can be a harsh chemical which can cause skin irritation. For regular swimmers, it can also be a respiratory irritant. [source]

Although chlorine is a strong pool chemical, it is essential for keeping our swimming pools clean. To date, there is no evidence to suggest that swimming in chlorine can cause dehydration.

Do You Lose Electrolytes When You Swim?

When you sweat, you lose not only water but also electrolytes. These are minerals such as sodium, potassium, magnesium and calcium that are essential for the body to function properly.

Swimming can cause you to lose electrolytes as you sweat. However, if you drink fluids that contain electrolytes, such as sports drinks with electrolytes, you can help replace what you have lost.

Some signs of electrolyte loss include muscle cramps, dizziness, and feeling faint. [source]

You can drink electrolytes before, during or after your swim.

Some recreational swimmers (myself included) are not big fans of some electrolyte sports drinks because of the high sugar content, but there are alternatives out there including natural foods where you can replenish your electrolyte stores.

If you are a regular swimmer, then having an electrolyte strategy is important to keep you feeling good. For more information on how to keep your electrolytes in balance as a swimmer, I recommend this article by Swimming World Magazine, which even gives us the electrolyte content of some foods.

What Are The Signs Of Dehydration?

Some of the most common signs of dehydration in adults and children include: [source]

  • Feeling thirsty
  • Dark yellow or strong-smelling pee
  • A dry mouth
  • Feeling dizzy
  • Headaches
  • Feeling tired

The signs of dehydration are difficult to spot as a swimmer. Being submerged in water, many of the most common signs of dehydration can be hidden, for example:

  • If water is getting into your mouth in the pool, a dry mouth will go unnoticed.
  • If you are sweating a lot, you will not notice this as the pool water will wash it away.
  • Headaches and dizziness can be blamed on poor technique or over-exertion.
  • Feeling tired can be blamed on working out too much.
  • Dry skin can be blamed on chlorine.

The above signs of dehydration can all be hidden from a swimmer, as our brains can trick us into believing we have plenty of water around us and don’t need any more. 

How Do You Prevent Dehydration When Swimming?

To prevent dehydration when swimming, it is important to drink plenty of fluids before, during and after swimming.

It is also important to eat foods that are high in water content, such as fruits and vegetables.

In addition, wear a swimming cap to keep your head cool and drink sports drinks that contain electrolytes to help replace the sodium and potassium you lose when swimming.

Most pools will allow bottled water to be left on the pool deck while you swim. Most pools will only allow bottled drinking water as this will not contaminate the pool if there is a spill, unlike a flavoured sports drink.

Here are some tips to keep hydrated while swimming:

1. Drink Before You Swim

Ensure you drink some water before you swim so you are already hydrated going into the pool.

2. Drink Cold Water

It is better to drink cold water as your body will absorb the cold water faster than it will absorb room temperature water.

3. Avoid Dry Mouth

It is a good idea to have the occasional sip of water while you are swimming. But do not over-drink to where you feel “full”. Ensure you sip regularly to avoid a dry mouth.

4. Drink Enough For Your Body

It is important to follow the basic water intake guidelines and add extra water on swim days. I use the following formula to ensure I am drinking enough.

Swimming Minimum Water Intake = (Body Weight (lbs)/ 2) + 16 fl oz

Here are instructions on how to use the above formula in practice.

  1. Measure your body weight in pounds.
  2. Divide your body weight by 2.
  3. Add 16 fl oz to that number.

The final number calculated with be the recommended minimum amount of water you should drink, measured in fluid ounces (fl oz) on a swimming workout day.

Final Thoughts

Swimming can be a great way to stay fit and healthy, but it is important to take precautions against dehydration.

It is very easy to forget or just not realise that we all sweat as we swim, since we might not notice sweat in the aquatic environment.

Just like working out in the gym, the more you exert yourself, the more you will sweat in the pool.

Drinking water before, during and after swimming is essential for preventing dehydration. In addition, eating foods that are high in water content can help.

Besides losing water, we also lose electrolytes as we swim. It is possible to drink sports drinks that contain electrolytes or electrolyte-specific drinks to help replace the sodium and potassium you lose when swimming.

By keeping hydrated in the pool, you can stay feeling fit and continue to enjoy your swimming workouts.

Happy swimming!

Louise Byrne

Hi, I am Louise and I am obsessed with swimming. I spend my free time in the water or getting ready for my next water adventure.

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