The Importance of Proper Hydration During Long Swim Sessions

Why You’re Losing More Fluid Than You Think — and How to Stay Fueled, Focused, and Fast 

You’re surrounded by water. You’re not dripping in sweat like a runner. You feel cool, refreshed, and “hydrated” just by being in the pool.

But here’s the truth: during long swim sessions, you are losing significant fluids — and if you’re not replacing them, your performance, recovery, and health are paying the price. 

Dehydration in swimmers is a silent saboteur. It creeps in unnoticed, masquerading as fatigue, poor technique, or “just a bad day.” Yet with simple, strategic hydration, you can maintain energy, sharpen focus, and finish strong — even in grueling 2-hour+ workouts.

In this guide, we’ll break down why hydration matters more than you think in the pool, how to recognize the signs of fluid loss, and — most importantly — how to hydrate effectively before, during, and after long swim sessions. 

💧 Why Swimmers Get Dehydrated (Even in Water)

1. You Sweat — A Lot 

• Competitive and distance swimmers lose 500–1000ml (17–34 oz) of sweat per hour during intense training.

• Chlorinated water evaporates quickly off the skin, hiding sweat evidence.

• Warm pools (82°F+/28°C+) and wetsuits (in open water) increase core temperature → more sweating. 

2. Thirst Cues Are Suppressed 

• Immersion in water reduces blood flow to the kidneys → less urine production → brain doesn’t trigger thirst as urgently.

• Cool water creates a false sense of “refreshment” without actual fluid replacement. 

3. Respiratory Fluid Loss 

• Rapid, deep breathing during intervals expels moisture — especially in dry indoor air.

• Hyperventilation before underwater sets? That’s fluid loss too. 

“Just because you don’t feel thirsty doesn’t mean you’re not dehydrated.”— Dr. Stacey Sims, Exercise Physiologist & Triathlon Coach  

🚨 Signs You’re Dehydrated During a Long Swim

Don’t wait for dizziness. Watch for these subtle red flags:

✅ Unusual fatigue or “heavy” limbs by mid-session

✅ Stroke technique breaking down faster than usual

✅ Heart rate staying elevated between sets

✅ Headache or brain fog after main set

✅ Dark yellow urine pre- or post-practice

✅ Dry mouth or cottonmouth during swim

✅ Muscle cramps — especially in calves, feet, or hands

⚠️ Even 2% dehydration can reduce aerobic performance by up to 10%. At 4%, cognitive function, coordination, and thermoregulation decline sharply.  

📅 Hydration Strategy: Before, During, After

➤ BEFORE Your Long Session (2–3 Hours Prior)

Goal: Start fully topped off — not playing catch-up mid-set.

• Drink 16–20 oz (500–600ml) of water or electrolyte drink

• Eat a light snack with sodium (e.g., banana + salted nuts, toast + peanut butter)

• Avoid caffeine or sugary sodas — they’re diuretics 

💡 Pro Tip: Weigh yourself before practice. Every pound lost later = 16oz fluid to replace.  

➤ DURING Your Long Session (Every 15–20 Minutes)

Goal: Sip consistently — don’t chug at the end.

• Keep a water bottle on deck — labeled, easy to grab between sets

• Sip 4–8 oz (120–240ml) every 15–20 minutes

• For sessions >75 minutes or high intensity: Use an electrolyte drink (low sugar, sodium + potassium focus) 

🥤 What to sip:    

• Plain water (for <60 min sessions)

• Electrolyte tabs in water (Nuun, Liquid IV, LMNT)

• Coconut water (natural option — but watch sugar)

• Homemade: 16oz water + pinch salt + squeeze lemon + tsp honey 

❌ Avoid: Sugary sports drinks (Gatorade, Powerade) unless racing >90 min — they spike insulin and upset stomachs.

💬 Coach Cue: “Hydration station between every 3rd set — no exceptions.”  

➤ AFTER Your Long Session (Within 30–60 Minutes)

Goal: Replace what you lost — fluids + electrolytes + glycogen.

• Weigh yourself again — drink 16–24 oz (500–700ml) per pound lost  

• Consume sodium-rich recovery snack within 30 min:

  • Chocolate milk (ideal carb + protein + sodium ratio)

  • Turkey sandwich + pickle

  • Smoothie with banana, yogurt, sea salt 

• Continue sipping water over next 2 hours 

📊 Example:

Pre-swim weight: 150 lbs

Post-swim weight: 148.5 lbs → Lost 1.5 lbs = Drink 24–36 oz fluids + salty snack  

🏊‍♀️ Hydration Tips for Different Long Sessions

🔹 Distance Sets (1500m–5000m) 

• Focus: Electrolytes during, recovery drink after

• Example: Sip Nuun every 20 min, chocolate milk post-set 

🔹 IM or Race-Pace Intervals (90+ min) 

• Focus: Aggressive rehydration + sodium loading between sets

• Example: Post-morning session → salty meal + 20 oz electrolyte drink. Pre-afternoon → 12 oz water + banana 

🔹 Masters/Recreational Long Swims 

• Don’t underestimate! Even “easy” 3000m burns fluids.

• Keep bottle on deck. Set phone timer to remind you to sip. 

🧂 Why Electrolytes Matter — Not Just Water

Sweat isn’t just water — it’s salt (sodium), potassium, magnesium, calcium. Lose too much, and you risk:

• Muscle cramps

• Brain fog

• Nausea

• Delayed recovery

• Hyponatremia (dangerously low sodium — rare but serious) 

✅ Best electrolyte sources for swimmers:    

• Salted snacks (pretzels, nuts, jerky)

• Electrolyte tablets (low/no sugar)

• Pickle juice (yes, really — proven cramp fighter)

• Bone broth (post-training recovery) 

🧒 Hydration for Young Distance Swimmers

Kids dehydrate faster — and rarely self-monitor.

✅ For parents/coaches:   

• Send swimmers with labeled water bottle

• Require sip breaks every 3–4 sets

• Offer flavored water (fruit-infused) if they resist plain

• Teach them to check urine color (“Pale = good. Apple juice = drink!”) 

🎯 Make it fun: “Hydration Hero” chart — sticker for every practice they finish their bottle.  

📱 Tech & Tools to Help

✅ Smart Water Bottles (HidrateSpark, Thermos Hydration Bottle) — glow or buzz to remind you to sip

✅ Urine Color Chart — post in locker room or team group chat

✅ Sweat Test Kits (like Precision Hydration) — calculate your personal sodium loss

✅ Wearable Hydration Trackers — some WHOOP or Garmin devices estimate sweat loss

🚫 Myths Busted

❌ “I’m in water — I can’t be dehydrated.” → FALSE. You absolutely can.

❌ “If I’m not thirsty, I’m fine.” → FALSE. Thirst lags behind need.

❌ “Sports drinks are best.” → FALSE. Most are too sugary for training. Save for races.

❌ “Coffee hydrates me.” → FALSE. It’s a mild diuretic — count it as half-fluid.

Sample Hydration Plan for a 2-Hour Distance Practice

6:30 AM — Wake up → 12 oz water + pinch salt

7:00 AM — Pre-swim snack: Oatmeal + banana + almond butter

7:30 AM — Arrive at pool → 8 oz electrolyte drink

During Practice (sip every 3rd set):   

• Set 1–3: 4 oz water

• Set 4–6: 4 oz Nuun

• Set 7–9: 4 oz water

• Set 10–12: 4 oz Nuun

  
  

  9:30 AM — Post-swim: Weigh in → drink 24 oz if down 1.5 lbs

  
  

  9:45 AM — Recovery: Chocolate milk + handful pretzels

  
  

  10:30 AM — Continue sipping 16 oz water over next hour 

Final Thoughts

Hydration isn’t glamorous. It doesn’t show up on the pace clock. But it’s the silent engine behind every strong pull, every crisp turn, every final sprint. Neglect it, and your body pays the price — in fatigue, cramps, slower times, and longer recovery.

So grab your bottle. Set your timer. Taste the salt. And remember:

The fastest swimmers aren’t just the strongest or most technical — they’re the ones who never let dehydration steal their edge.  

Sip. Swim. Repeat. 

Because champions aren’t made in the lane — they’re made in the moments between, one ounce at a time. 💦🏊‍♂️💙