A blog by runners. For runners.

Hydration 101: get the facts

Our bodies are made up of mostly water. When we take in less water than we put out, dehydration happens. Dehydration causes our bodily systems to stop working well. Slight dehydration can hinder an athlete’s performance and severe dehydration can cause death. That’s why it’s so important for runners and cyclists to drink plenty of fluids.

How much water should runners drink?

The Institute of Medicine recommends men drink about 13 cups of water each day, and women aim for 9 glasses of water per day. However, it said you need even more liquids when it’s hot and humid out and during and after exercise, meaning athletes need more than this recommendation.

Don’t wait until you feel thirsty to drink up. Our thirst sensation doesn’t kick in until we’re already dehydrated. So, it’s important to drink enough before, during, and after activity. Following these guidelines can help ensure you’re drinking enough H2O:

Before a run: Drink 8-16 oz. of water 1-2 hours before a run. Or take in 4-8 oz. of fluids 15-30 minutes before heading out.

On the run: Your fluid needs during a run depend on how long your exercise session lasts:

    • Under one hour: Drink 3-6 oz. of water every 15-20 minutes. If you’re exercising intensely for more than 30 minutes, drink a sports drink instead.
      • 1-4 hours: Drink 3-6 oz. of a sports drink (to replenish electrolytes) every 15-20 minutes. If you prefer meeting your electrolyte needs with gels or chews, chase them down with plenty of water.
      • Over 4 hours: Drink 3-6 oz. of sports drink every 15 minutes and pay attention to your thirst sensation. Drink more often if you’re thirsty, and less often if you’re not.

Post-run: Take in enough liquids so that you need to use the bathroom within 60-90 minutes after a run. Usually 8-24 oz. of fluids is enough.

How can I tell if I’m drinking enough water?

Everyone’s fluid needs are different. Weighing yourself before and after a run can help gauge if you drank enough during your workout. If you weigh the same at both times, you’re drinking enough water on your run. But if you weigh two pounds less, you’re dehydrated. For every pound you lose, you need an extra 16 oz. of fluid. To avoid the two pound weight loss next time, you’ll need to take in an extra 32 oz. of liquids on your run.

The color of your urine is also a good indicator of hydration. A pale yellow color means you’re probably getting enough water.

What are the symptoms of dehydration?

The following are signs of dehydration:

  • Increased thirst
  • Weakness, dizziness, and confusion
  • Feeling sluggish or fainting
  • Dry mouth and swollen tongue
  • Palpitations (feeling like your heart is jumping)
  • Inability to sweat
  • Low urine output or deep yellow or amber-colored urine.

If you experience signs of dehydration, stop running and rehydrate.

Can you drink too much water?

Yes. Marathon runners, in particular, are at risk for a rare, life-threatening condition called hyponatremia. Hyponatremia occurs when there is too little sodium in the blood, and it happens as a result of drinking too much water. That’s why endurance athletes need to rehydrate with sports drinks because they contain sodium and other vital electrolytes.

Written by Jenilee Matz, MPH. Jen is writer, runner, and new(ish) mom living in the suburbs of Charlotte, N.C.