How Much Should Runners Drink?

Hydration advice gets weird fast. Drink too little and the run falls apart. Drink too much and you can create a different problem entirely.

Imagine you're out for a run, sweating and in the zone. Suddenly your mouth feels a little dry. You reach for your water bottle, and... you're out of water. If you're like most people, your brain starts chanting one word: water. Water. Water!

Take a second and pause. The full picture is more interesting than "more water, always."

Let's be clear: water is important. Your blood, muscles, and brain are mostly water. It regulates body temperature, moves oxygen and nutrients to your muscles, and flushes out waste. Well-hydrated runners can go longer and harder than dehydrated ones. No argument there.

The questions are trickier: how much should you drink before a run, and will you get in trouble if you don't drink enough? The answers are not as straightforward as your high school gym teacher made them sound. When athletes collapse in hot races, investigators end up looking at sweat rates, humidity, environmental conditions, drinking habits, and physical limits. It's rarely one simple thing.

Dehydration is real

If you go into a run under-hydrated, especially a long or hot one, you can have a serious problem. Thirst, fatigue, cramping, and a fading pace are your body asking for fluid it should have gotten hours ago.

But while not drinking enough is bad, the opposite is also true.

Too much water can be fatal

This is the part most runners have never been told. Hyponatremia is a condition in which the sodium level in your blood drops dangerously low. One way runners get there: drinking large amounts of plain water while sweating out sodium, diluting what's left. Symptoms include:

• Muscle cramps
• Nausea and vomiting
• Headache and confusion
• Seizures
• Unconsciousness
• And yes, death

The people most at risk are often newer runners who've absorbed "hydrate!" as the only rule. You've probably seen someone at a 5K wearing a full hydration backpack, or met the marathon trainee who brags about drinking five gallons a day. Make no mistake: too much water can be dangerous, and drinking to a schedule instead of to your body is how people get there.

So how should you hydrate?

A few guidelines that hold up:

• Drink throughout the day, every day. Arriving at a run well hydrated matters more than chugging at the start line.
• Drink to thirst on the run. For most runs in most conditions, thirst is a decent guide, and it's much better at preventing overdrinking than a forced schedule.
• Long or hot runs need a plan, not just thirst. Over roughly an hour, or in serious heat, sweat losses climb and thirst can lag behind. Carry fluids, sip regularly, and include electrolytes, not just plain water. There's a reason sweat tastes like salt. (You know it's true, even if you found that out by accident.)
• Skip the folklore numbers. The old "64 ounces a day" rule is a rough average, not a law. If you're a casual 5K-now-and-then runner eating normal food, ordinary daily drinking probably covers you. If you're logging long summer miles, it won't.

If sports drinks aren't your thing, fruit-infused water plus salty food gets you most of the way there for moderate runs.

Heat changes all of this math, by the way. Sweat rates in summer can be dramatic; we covered what heat does to a running body in Running in the Heat.

Note: this is from one runner to another, not medical advice. If you have kidney issues, take medications that affect fluid balance, or have ever had trouble regulating sodium, talk to a doctor before you take hydration strategy from a running blog. Honestly, that's good advice for everyone.