Halfway through a long meet in Victoria, I looked over and noticed Rafa's water bottle was still completely full. It was noon. She had already raced twice, warmed up, warmed down, and the bottle had not been touched. When I asked her about it she looked at me like I was crazy â "Dad, I'm literally in water all day. Why would I be dehydrated?" That moment was a wake-up call for me, and probably for a lot of swim parents who assume the pool takes care of hydration.
Here is the thing: it does not.
There is a common myth that swimmers do not sweat because they are in water. They absolutely do. According to the American College of Sports Medicine (ACSM) position stand on exercise and fluid replacement, adequate hydration is essential for maintaining health, safety, and optimal athletic performance. Competitive swimmers can lose between 500 millilitres and over a litre of sweat per hour of intense training. The cool water masks the sensation, but the fluid loss is real, and it affects performance more than most families realize.
A 2015 study by Arnaoutis et al., published in the Journal of the International Society of Sports Nutrition, found that 89.8% of young athletes arrive at training already hypohydrated â and only 16.6% of young swimmers begin practice properly hydrated. If your child finishes practice feeling sluggish, headachy, or unusually tired, dehydration might be part of the picture.
Yes, You Sweat in the Pool
During a hard practice, your child's core temperature rises just like it would in any other sport. Research by Shaw et al. (2014), published in PMC, found that swimmers' energy demands are 25-100% higher than non-athletes, which means their bodies are working significantly harder and losing more fluid. The body responds by sweating to cool down. Because the pool water washes the sweat away immediately, swimmers rarely notice it happening. This makes swimming one of the sneakiest sports for dehydration. By the time a swimmer feels thirsty, they are already behind on fluids.
How Much to Drink: Before, During, and After
A simple framework can help your swimmer stay on top of hydration.
- Before practice (2 hours out): 400 to 500 ml of water. This gives the body time to absorb the fluid before getting in the pool.
- During practice: 200 to 300 ml every 15 to 20 minutes. Most coaches allow water bottle breaks at the wall. If your child's coach does not, it is worth a respectful conversation about it.
- After practice: At least 500 ml within the first 30 minutes. If practice was especially long or intense, more is needed.
These are general guidelines. Larger swimmers, hotter pool environments, and longer sessions all increase the need.
Signs of Dehydration to Watch For
Dehydration does not always announce itself dramatically. The early warning signs are subtle:
- Dark yellow urine (healthy hydration produces pale, straw-coloured urine)
- Headaches during or after practice
- Muscle cramps, especially in the calves or feet
- Unusual fatigue or sluggishness in the water
- Dizziness or lightheadedness when standing on the blocks
If your child reports any of these regularly, hydration habits are the first thing to examine.
What to Drink
For most practices under 90 minutes, plain water is the best choice. It is simple, effective, and does not come with added sugars or artificial ingredients.
For longer or more intense sessions, an electrolyte drink can help replace the sodium and potassium lost through sweat. Look for options that are low in sugar. Many sports drinks on the market contain as much sugar as a soda, which can actually work against hydration by slowing fluid absorption.
What to avoid: sugary sodas, energy drinks, and anything with high caffeine content. These can cause energy crashes, stomach discomfort, and actually increase fluid loss.
Meet-Day Hydration
Meet days are long. Your child may be at the pool for six to eight hours but only race for a few minutes total. The biggest mistake families make is waiting until race time to think about hydration.
Start hydration the day before. Make sure your swimmer drinks consistently throughout the meet, not just before their events. Keep a water bottle in their bag and set gentle reminders if they tend to forget. Pair hydration with light snacking to keep electrolyte and energy levels steady.
Avoid the temptation to rely on the concession stand. Most of what is sold there falls squarely in the sugary-drink-and-heavy-snack category.
Build the Habit Early
The best thing you can do is help your swimmer build hydration into their routine so it becomes automatic. A water bottle packed in the swim bag every day. A glass of water first thing in the morning. A post-practice drink on the drive home.
These small habits add up. A well-hydrated swimmer recovers faster, trains better, and feels stronger in the water.
Gophin helps families track swimming progress with clarity. Try it free at gophin.app.
Sources
- 1. Arnaoutis, G. et al. (2015). "Hydration status of young athletes." 89.8% of young athletes hypohydrated pre-training; only 16.6% of young swimmers properly hydrated. Journal of the International Society of Sports Nutrition.
- 2. American College of Sports Medicine (ACSM). Position stand on exercise and fluid replacement. Adequate hydration maintains health, safety, and optimal performance.
- 3. Shaw, G. et al. (2014). "Nutrition for swimming." Swimmers' energy demands 25-100% higher than non-athletes. PMC.
