Hydration for Swimmers: A Rehydration Plan for Imperceptible Fluid Loss During Training

Introduction

“How could I possibly get dehydrated while swimming in water?” This is one of the most common misconceptions among swimmers. Fluid loss comes from sweating and breathing—whether or not you’re submerged in water, as long as your body is working hard, fluid keeps being lost. Research shows that swimmers lose 0.5–1.5 liters of sweat during a 60–90 minute training session, and even more in hot environments (such as indoor pools during Taiwan’s summer). What makes it trickier is that buoyancy keeps you feeling cool, so your brain doesn’t easily register the actual state of dehydration—by the time you feel thirsty, you’re often already mildly dehydrated.

The Impact of Dehydration on Swimming Performance

The degree of dehydration is directly proportional to its impact on performance:

For a 60 kg athlete, 1% dehydration equals a loss of approximately 600 ml of body fluid. A 90-minute training session with no fluid intake at all can easily reach 2% dehydration.

Hydration Plan Before, During, and After Training

2–3 hours before training:

• Drink 500–600 ml of water
• Urine color target: pale yellow (straw-colored)
• If urine is dark yellow or orange, it indicates mild dehydration—increase water intake

During training:

• Replenish 150–250 ml every 15–20 minutes
• For sessions exceeding 60 minutes, consider a sports drink with electrolytes (diluted version)
• Rest intervals (between sets, during technique instruction) are good opportunities to hydrate
• Keep a water bottle at poolside and make it a habit to drink every time you stop

Within 2 hours after training:

• Replenish 150% of the fluid lost during training (e.g., if you lost 500 ml, drink 750 ml)
• Pair with sodium-containing foods to promote fluid retention

The Importance of Electrolytes

Long-duration swimming depletes not only water but also electrolytes:

• Sodium: Maintains extracellular fluid balance; the first thing to replenish after heavy sweating
• Potassium: Essential for muscle contraction; deficiency can easily trigger cramps
• Magnesium: Supports neuromuscular function; chronic deficiency is linked to nighttime cramps
• Chloride: Works with sodium to maintain fluid balance

Sports drinks (such as舒跑 or 開喜運動飲料) contain adequate electrolytes and are suitable for training sessions over 60 minutes. However, note that commercial sports drinks are high in sugar—if your session is under 60 minutes, plain water is sufficient.

Local Taiwanese hydration options:

• Coconut water: naturally rich in potassium, suitable for post-training recovery
• Honey water with a pinch of salt: a homemade simple sports drink
• Plum juice (watch the sodium content): a traditional Taiwanese electrolyte option

Practical Tips

• Establish a habit of weighing yourself before and after training: if your post-training weight is more than 1 kg lighter than pre-training, you need to hydrate more aggressively
• Taiwan’s summer indoor pools are hot and poorly ventilated, causing sweat rates far higher than in winter—increase fluid intake accordingly
• Race-day hydration strategy should mirror training; never try new drinks or hydration methods on race day
• For long-distance swim training or open-water sessions, keep sports drinks at poolside or on the support boat
• Drink a large glass of water (about 300–500 ml) immediately upon waking to replenish overnight fluid loss
• Avoid overhydration (Hyponatremia, low blood sodium): consuming excessive plain water without sodium replacement can dilute blood sodium levels—pay special attention after ultra-long-distance events

Conclusion

Hydration management for swimmers is a severely underestimated training component. The “invisible loss” in the water leads many athletes to mistakenly believe they don’t need to actively hydrate. Establishing a before-during-after hydration routine for every session, paired with appropriate electrolyte supplementation, not only maintains training quality but also reduces cramp risk and accelerates recovery. Keep that water bottle at poolside and make hydration a standard part of every workout.

Related Reading

• Hydration Strategies in Swimming: The Hidden Dehydration Risk of Water Sports
• Fluid Replacement in Swim Training: The Hydration Challenge in Chlorinated Water
• Fluid and Electrolytes for Swimmers: Replenishment Strategies for Long-Duration Swimming
• The Science of Fluid Replacement: How to Calculate Your Personal Sweat Rate and Hydration Needs