Hydration Mistakes to Avoid This Summer 6/15/26

You drank water all day. You had a bottle before your run. You felt fine going out the door. And then somewhere around mile three you felt like you were running through wet concrete with a headache forming behind your eyes and your legs suddenly weighing twice what they should.

You weren’t dehydrated when you left the house. But you were already behind before you ever laced up.
This is the most common hydration mistake runners make in the summer, and it’s not the only one. Let’s go through them—because getting this wrong in June in Knoxville isn’t just uncomfortable. It’s a real performance and safety issue.

The biggest misconception is that hydration is a during-the-run job. It isn’t. By the time you feel thirsty, you are already in a deficit. Thirst is a late signal, not an early warning system. Drinking reactively—waiting until you’re dry-mouthed on mile two to start thinking about fluids—means you’re spending the rest of your run playing catch-up with a system that’s already compromised. Hydration is a before-the-run job. It’s a all-day job. It starts when you wake up, not when you head out the door.

The second mistake is drinking only water. Water is essential, but in the summer—especially during longer efforts or for runners who sweat heavily—water alone doesn’t cut it. Without electrolytes, particularly sodium, your body can’t retain or effectively use the fluid you’re taking in. You can drink plenty of water and still end up functionally under-hydrated because you’re missing the minerals that make hydration actually work. This is why electrolyte drinks, tablets, or even salty foods matter more in summer than any other time of year. Water hydrates. Electrolytes help your body hold onto it.

Know Your Own Body

Here’s something that doesn’t get said enough: hydration is individual. Some runners sweat more than others. Some lose significantly more sodium in their sweat—you may have seen the white residue on your skin or your hat after a long run. That’s salt loss, and it matters. A hydration strategy that works perfectly for your training partner may leave you cramping and dizzy because your needs are genuinely different from theirs.

Pay attention to your own signals. How much do you sweat? How do you feel at mile four versus mile one? Are you cramping? Are you finishing runs feeling wrecked in a way that goes beyond normal fatigue? These are data points. Use them to build a hydration approach that’s specific to you rather than borrowed from a generic formula.

Front-loading fluids right before you head out is another trap. Drinking a large amount of water in the hour before your run does not make up for a day of under-hydrating. Your body can only absorb and utilize fluid so quickly, and arriving at the start of your run with a stomach full of water you just chugged is not the same as arriving well-hydrated. Hydration is cumulative. It builds throughout the day. A useful starting point is to aim for half your body weight in ounces of water daily—more on heavy training days and more in the summer heat or if you know you’re a heavy sweater—spread across the entire day rather than concentrated around your run.

And don’t stop thinking about hydration the moment you stop moving. The deficit you built during a summer run doesn’t close the second you hit stop on your watch. What you drink in the hour after a run matters as much as what you drink during it. Prioritize fluids and electrolytes post-run, not just a celebratory gulp of water before you move on with your day.

What Good Summer Hydration Actually Looks Like

Start hydrating when you wake up. Carry water consistently throughout the day. Add electrolytes to at least one bottle daily—more if you’re running long or sweating heavily. Go into your run already hydrated, not hoping to catch up during it. Drink during your run if it’s over forty-five minutes or if conditions are particularly brutal, which in Knoxville in July is most days. Rehydrate intentionally after you finish.

It’s unglamorous. It’s not a particularly exciting topic. But hydration might be the single most impactful thing you can do for your summer running, and it’s almost entirely within your control. Get it right and everything else—the pace, the effort, the recovery—gets a little easier.

The heat is going to do what the heat does. Don’t make its job easier by showing up unprepared.

-Brittany Kellogg, CPT, CSNC