Dehydration

It’s important to drink adequate water when you’re hiking in hot weather to prevent dehydration. Dehydration can leave you feeling crummy and possibly contribute to other heat-related illnesses, such as cramps, heat exhaustion and heat stroke.

How much you need to drink while hiking depends on a number of factors, such as temperature and humidity, your intensity level, your age, your body type and sweat rate, as well as the duration of your hike. A good general recommendation is about a half liter of water per hour of moderate activity in moderate temperatures. From there, you may need to increase how much you drink as the temperature and intensity of the activity rise. For example, strenuous hiking in high heat may require that you drink one liter of water or more per hour. As you gain experience, you’ll be able to fine-tune how much you drink.

Overhydration

The flip side to dehydration is overhydration, or hyponatremia. This is a fairly rare condition that mainly affects endurance athletes such as marathon runners, ultrarunners and triathletes, but it’s something that hikers should be aware of.

In hyponatremia, sodium levels in the blood become so diluted that cell function becomes impaired. In very extreme cases, hyponatremia may cause coma and even death.

The symptoms of hyponatremia are similar to dehydration: fatigue, headache and nausea, causing some athletes to mistakenly drink more water and exacerbate the issue.

Preventing overhydration: The key to preventing overhydration is to monitor how much you drink.

  • Don’t overdrink—Stick to drinking a few gulps of water about every 15–20 minutes and try not to drink more than you sweat. Weight gain during exercise is a telltale sign that you’re drinking too much.
  • Add salt—Keep your salt levels balanced by occasionally drinking a sports drink with electrolytes instead of plain water and/or eating a salty snack, such as pretzels. You can also take salt tablets.