How to Stay Hydrated During Swim Training

Why You Sweat More Than You Think — and How to Fuel Your Performance from the Inside Out 

You’re surrounded by water. You’re not dripping in sweat like a runner or cyclist. So… you must be hydrated, right?

Wrong. 

Swimmers are among the most chronically dehydrated athletes — and many don’t even realize it. The cool water masks sweat loss. The absence of visible perspiration tricks the brain. But make no mistake: during intense swim training, your body is losing fluids, electrolytes, and performance potential with every lap.

In this guide, we’ll break down why hydration matters more than you think in the pool, how to recognize dehydration before it sabotages your set, and — most importantly — how to hydrate strategically before, during, and after swim training to boost endurance, recovery, and overall health.

💧 Why Swimmers Get Dehydrated (Even in Water)

1. You DO Sweat — A Lot 

• Studies show competitive swimmers lose 500–800ml of sweat per hour during moderate to high-intensity training — comparable to cyclists and runners.

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

• Wetsuits (in open water) or warm pools increase core temperature → more sweating.

2. Thirst Mechanism Is Suppressed 

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

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

3. Breathing Hard = 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, Sports Physiologist & Triathlon Coach  

🚨 Signs You’re Dehydrated in the Pool

Don’t wait until you’re dizzy. Watch for these subtle red flags:

✅ Fatigue hits earlier than usual

✅ Stroke technique breaks down faster

✅ Heart rate stays elevated between sets

✅ Headache or dizziness after main set

✅ Dark yellow urine pre- or post-practice

✅ Dry mouth or cottonmouth during swim

✅ Cramps — especially in calves, feet, or hands

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

📅 Hydration Strategy: Before, During, After

➤ BEFORE Training (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 Training (Every 15–30 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 Training (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 lbsPost-swim weight: 148.5 lbs → Lost 1.5 lbs = Drink 24–36 oz fluids + salty snack  

🏊‍♀️ Hydration Tips for Different Swim Sessions

🔹 Sprint/Interval Workouts (<60 min)

• Focus: Water + light sodium pre/during

• Example: 12 oz water + pinch of salt in bottle

🔹 Endurance Sets (1–2 hours)

• Focus: Electrolytes during, recovery drink after

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

🔹 Double Practices or Meets

• Focus: Aggressive rehydration + sodium loading between sessions

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

🔹 Masters/Recreational Swimmers

• 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 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.  

❄️ Cold Water ≠ Hydration

Jumping in a cold pool may feel refreshing — but it doesn’t rehydrate you. In fact, cold immersion can further suppress thirst cues. Always drink — even if you feel “cooled off.”

📱 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 90-Minute Masters Practice

7:00 AM — Wake up → 12 oz water + pinch salt7:30 AM — Pre-swim snack: Oatmeal + banana + almond butter8:00 AM — Arrive at pool → 8 oz electrolyte drinkDuring Practice (sip every 3rd set):   

• Set 1–3: 4 oz water

• Set 4–6: 4 oz Nuun

• Set 7–9: 4 oz water

  
  

  9:30 AM — Post-swim: Weigh in → drink 20 oz if down 1 lb

  
  

  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. 💦🏊‍♂️💙