Why Swimmers Can Get Dehydrated (Easy Explanation)


Every athlete that participates in physical activity on a regular basis is at risk for dehydration if they fail to take the proper precautions. But does the risk for dehydration change from land-based activities to water-based activities?

Swimmers can get dehydrated as they sweat persistently in response to a rise in core body temperature. Pool water cannot rehydrate swimmers since the skin is unable to absorb water from the environment. Dehydration is a greater risk for swimmers because monitoring sweat loss is more difficult.

Put simply, swimmers can get dehydrated just like any other common athlete. To learn more about how swimmers get dehydrated, along with information regarding how to detect early symptoms of dehydration, read on.

How Swimming Can Make You Dehydrated

There are several reasons behind why swimmers are not immune to the negative effects of dehydration. Some of these reasons are universal to all athletes, while others are specific to the sport of swimming.

The Body Sweats Naturally as Core Temperature Elevates

A large portion of the population is under the mistaken impression that swimmers are incapable of sweating simply because they’re surrounded by water. The truth of the matter is that swimmers do sweat. In fact, they lose a great deal of fluid because they sweat.

As swimmers physically exert themselves in the water, the body is forced to manufacture more energy to fuel this activity. This increased energy production results in excess body warmth, as heat is a natural by-product of this metabolic process. To keep a stable core body temperature—otherwise known as maintaining homeostasis—the body must employ certain physiological mechanisms to rid the body of this excess heat.

There are two main strategies that the body uses to rid the body of excess heat (source):

  • Sweat Evaporation – The body takes advantage of the large amount of surface area on the skin by sweating. As fluid gathers on the skin and evaporates, internal heat is dispelled as well.
  • Reinforcing Blood Flow to Skin – Warm blood is intentionally directed toward the skin. The sweat lingering on the surface of the skin cools down this warm blood. Consequently, the warming effects that result from reinforced blood flow to the skin is counterbalanced by the cooling effects that result from sweating.

Since our main focus will be on the dehydration effects of swimming, sweat evaporation will be our primary concern, as this body response is the underlying culprit behind why swimmers get dehydrated in the first place.

When swimmers progress into the latter portions of the workout, heat accumulates to a large degree as a by-product of constant physical exertion. Contrary to popular opinion, the surrounding pool water is not enough to regulate core body temperature. Internal body heat heightens as a direct consequence of physical activity, regardless of whether a swimmer’s body is surrounded by water or not.

Thus, the body begins to sweat even more vigorously, depleting any fluid reserves left. If these fluid reserves are not replenished, dehydration results. Unfortunately, the issue of replenishing these fluid reserves is not as obvious to swimmers as it would seem, as we’ll discuss in the next section.

Tough to Discern How Much Sweat Has Been Lost

Being surrounded by water, you would think that dehydration would be the least of your worries. Sadly, this is not the case. Once you immerse yourself in pool water and work out for a prolonged period of time, it’s hard to judge exactly how much sweat you’ve produced over the course of the swimming session. As a result, many swimmers underestimate how much fluid they’ve truly lost.

Consequently, swimmers fail to take the necessary steps to replenish their fluid reserves and ward off dehydration during their work out. It is only after the exercise that they begin to realize the folly of their inaction. By this time, it’s often too little, too late.

Fortunately, most seasoned swimmers are intimately familiar with the dehydration risks associated with prolonged bouts in the water. Typically, it is the casual, inexperienced swimmer that is at the highest risk for dehydration, as they’re the ones that overlook how serious of a threat dehydration can be in the pool.

Failing to Hydrate Prior to Lengthy Swimming Sessions

Another major contributor to dehydration in swimmers is the fact that many people fail to drink a sufficient amount of water before the workout itself.

As emphasized previously, swimmers are already at a greater risk for dehydration because of how difficult it is to monitor sweat loss. With a swimmer that fails to drink enough fluid pre-workout, this effect is compounded even further.

Just like any other physical activity, it’s important to hydrate adequately prior to swimming. You should not abstain from drinking fluids because you’re entering the pool. Submerging yourself in pool water will do nothing to help your hydration status.

Why People Mistakenly Believe Swimming Cannot Cause Dehydration

The misconception that swimmers cannot suffer from dehydration originated from the idea that pool water can serve as a source of hydration. This notion could not be further from the truth.

As touched on previously, the skin cannot soak up water like a sponge. The skin is meant to act as a protective waterproof barrier to the external environment (source). The skin is not designed for the purpose of hydration. The only way to naturally hydrate is to drink fluids.

Plus, pool water would not be ideal for staving off dehydration anyways with all of the circulating chemicals meant to kill bacteria. For example, the high concentration of chlorine in pool water is toxic to the human body when consumed, leading to chlorine poisoning (source). This is why drinking pool water is an ill-advised practice, as it does more harm than good.

How to Spot Signs of Dehydration While Swimming

Due to the slightly increased risk of dehydration in swimmers, it is important to be familiar with the early signs of dehydration. This way, you can take appropriate action before you, or one of your swimming peers, suffer the consequences.

Early signs of mild to severe dehydration include, but are not limited to (source):

  • accelerated breathing
  • dizziness
  • dry mouth
  • flushed skin
  • headache
  • lightheadedness
  • persistent thirst
  • pounding heart
  • sunken eyes
  • unexplained fatigue

If dehydration becomes too severe, it may not be possible for a swimmer to rehydrate by drinking fluids alone, particularly if diarrhea or vomiting results.

Under these circumstances, seek medical help immediately, as proper rehydration may only be possible through fluids distributed intravenously. As a quick reference, intravenous fluid administration is when a small tube is embedded into a vein—typically in the arm or hand—to inject critical fluids and electrocytes back into circulation (source).

Ideally, you want to take proper precautions to avoid this dire scenario, a topic that will be discussed in greater detail next.

Ways to Prevent Getting Dehydrated from Swimming

Although dehydration is a real possibility for swimmers, this does not mean that your fate is completely out of your hands every time you hit the pool. There are strategies that you can implement to greatly reduce your risk for dehydration when swimming. The most prominent of which are listed below.

Drink 8 oz of Fluid for Every 20 Minutes of Swimming

The biggest issue that swimmers face is not drinking enough water before, during, and after their workouts. Since they are not aware of how much fluid they’ve lost through sweating, it is fairly easy to forget to consciously stop and take scheduled water breaks throughout the swimming session.

For this reason, it is crucial to set fixed breaks throughout the workout to allow yourself time to properly rehydrate. Otherwise, you will simply forget to replenish your fluids and pay the price later.

As a general rule of thumb, you should aim to drink 8 oz of fluid for every 20 minute interval that you actively swim. By keeping an internal clock of exactly when you need to rehydrate, you’re much more likely to stave off the risk of dehydration. It may not even be a bad idea to bring a timer along with your water bottle to maintain a fixed hydration schedule.

To completely refuel your body, you may even want to consider rehydrating with a sports drink as opposed to pure water. Sports drinks are often infused with electrolytes to provide the body with the chemical substances it needs to perform essential metabolic functions.

If the electrolyte balance is lost, research has shown cognitive and physical performance to experience a significant decline, detracting from the overall effectiveness of your swimming session (source).

Swim in Pools Chilled Between 77 to 82℉

Another effective way to prevent dehydration is to swim in pools that are chilled to cooler temperatures.

Competitive swimming pools are chilled to cooler temperatures of 77 to 82℉ for a reason (source). The seemingly frigid waters help to regulate the core body temperatures of competitive swimmers by cooling warm blood near the skin and minimizing the need to sweat. Thus, swimmers sweat less in cold water than what they normally would in warm water.

This phenomenon was confirmed in a recent research study where the effects of three various water temperatures (23, 27, and 32°C) were measured on competitive swimmers. In this study, dehydration was monitored by taking into account variables such as sweat rate, urine output, and plasma electrolytes among others. From the data gathered, researchers concluded that dehydration shows a statistically significant upward trend as pool water temperature rises (source).

Conservation of fluids by sweating less is key to being sufficiently hydrated. Whenever you plan on taking on a particularly rigorous workout, you should look to swim in these chilled lap pools. Typically, recreational pools are slightly warmer than lap pools to accommodate for younger children. This slight temperature increase may not seem like much, but it can make a big difference in your hydration status over the course of a workout.

When swimming in open water under the rays of the hot sun, you should take extreme precaution to monitor your hydration levels. In these conditions, dehydration is a far greater risk since the hot weather and warm water will be working against you. Not only that, but hyperthermia can emerge as a major issue as well.

To learn more information about how swimming can lead to hyperthermia, click over to Why Your Body Feels Hot After Swimming (Explained!).

In summary, swim in cold water as much as possible! It may feel uncomfortable when you first get in, but it’s well worth the trouble in the long run.

The Bottom Line

Swimmers can suffer from dehydration, contrary to popular opinion. In fact, they’re often at a greater risk for dehydration compared to land-based athletes because they have no way of knowing how much fluid they’ve lost through sweat.

For this reason, it’s important to know the early signs of dehydration as well as what preventative measures to maintain a healthy level of circulating fluid.

All content written by HydroPursuit is for informational purposes only. The material found on this site is not intended to replace professional medical advice, treatment, or diagnosis. Consult with an accredited health care provider prior to initiating a new health care regimen.

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Austin Carmody

I am the owner of HydroPursuit. I enjoy kicking back and getting out on the water as much as I can in my free time.

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