How Long Can You Survive Without Water?

Ashley Thess

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Every team at your favorite bar’s trivia night might get this question right: How long can you survive without water? The rule of three when it comes to survival is common knowledge. You can survive three minutes without air, three days without water, and three weeks without food. But tragic stories hit the news every year when a runner doesn’t come back from their trail run or a family doesn’t return from their day hike. Heat and physical exertion drastically affect how long you can actually survive without water. Any outdoor enthusiast should know the risks, variables, and solutions when it comes to how long you can survive without water.

Risks of Dehydration

This PSA about dehydration is posted in the Zion National Park shuttle buses that run through the park all summer. Ashley Thess

Thirst is the first symptom of dehydration, so if you’re thirsty, you’re already dehydrated. A few things start to happen when we get dehydrated. Your kidneys start to retain water, causing infrequent and darker urination. You also sweat less, causing your body to overheat. 

As your blood thickens, your cardiovascular system works harder to keep your blood pressure up and your body receives less oxygen. This starts to affect your mood, thinking, physical performance, and ability to cool down through sweating. This is a very dangerous state to be in, especially if you’re in the wilderness or exercising in the heat. Your risk for heart attacks and seizures rises. You’ll also be less physically capable of getting yourself to a water source as your muscles cramp and joints stiffen. If you’re unable to rehydrate, your body will start to experience organ failure and eventually death.

How Long Can You Survive Without Water? It Depends …

Once you’re dehydrated, there are a number of factors that contribute to how long you can survive without water. Age, activity levels, overall health, height and weight, and sex are some characteristics that determine how long you can go without water. Circumstantial variables also come into play like what you drank and ate that day, how much you’re exercising, and heat. Let’s look at how some of these factors affect the average estimate of three days being the longest you can go without water.


In direct sunlight, high heat, and high humidity, your body is dispelling water through sweat so that it evaporates and carries away heat, providing a cooling effect. However, if you’re dehydrated you might sweat less, losing the ability to cool your body. In humid environments, sweat doesn’t evaporate efficiently because the air is already saturated. This can cause your body to lose even more water and overheat. You might only survive a few hours if your body is overheating and dehydrated.


Medications and medical conditions can decrease your survival time without water. The most serious water survival situation I’ve encountered was thanks to an unforeseen health issue. Four of us embarked on a canyoneering trip with 2 liters of water each. After a hot, sandy, and exposed approach through the desert, we finally arrived at the advanced canyon we expected to disappear into for the next 9-14 hours. But one person in our group was already out of water. 

It turns out, antidepressants and other medications can greatly increase your water consumption. After much sharing of water, a useless clogged filter, and two rappels, our friend was dry heaving. She didn’t even have enough water in her body to throw up. Her blood toxicity levels were dangerously out of whack with the recipe of strong medication, heat, physical exertion, and lack of water. 

Be aware of medications that increase urination or dehydrate your body. Vomiting and diarrhea from dehydration can make the situation more dire as you continue to expel water that you can’t afford to lose. Take these symptoms very seriously and find water ASAP.

Height and Weight

Typically larger people will need more water. Similarly, men usually need more water than women, unless they are pregnant or breastfeeding. Take this into account when you ask your friends how much water they are packing; everyone is different and has different hydration needs. Make note of how much water you’re drinking and in hot environments, pack more than you think you need.

What You Drank or Ate

Some foods are high in water content like watermelon, cucumbers, and celery. These snacks offer more hydration. However, foods that are dry or high in sodium will dehydrate you. If you’re already dehydrated and without water, be thoughtful about what you eat. Your body uses water in the digestion process, and you want to conserve as much as possible.

Alcohol also dehydrates you. If you plan on packing a summit cocktail, make sure to supplement with extra water. If you’re dehydrated, skip the booze altogether. Caffeine is a diuretic meaning it can increase urination, but experts say the fluid in caffeinated beverages should equal out the water you expel. However, if you’re trying to rehydrate, skip the caffeine and opt for electrolytes.

Tips for Staying Hydrated in the Wilderness

Bring More Than Enough Water

As a general rule of thumb, it’s recommended you bring 1 liter of water per hour of hiking. While backpacking this August, I encountered a 13-mile stretch of trail where there were no opportunities to filter drinkable water. I carried 6 liters of water, even though I only expected to drink two. 

With only 2 miles to my next water source, I was rattled by a rattlesnake in the middle of a field of tall desert grasses. Jumping backwards, I made a lot of noise until it slithered away, but it’s a situation exactly like that why you carry extra water. Had the snake bit me, it would have been even more dangerous if I didn’t have enough water.

Filling up my water filter bag from a natural spring. Ashley Thess

You can also bring a water filter or water filtering water bottle while day hiking, in case you run out. This way you can re-up your supply if necessary, without getting sick. Keep extra water in your car so that you can rehydrate post-hike, even if you’re miles from a gas station or water fountain. 

Read Next: The Best Backpacking Water Filters of 2023

Gear to Keep You Hydrated

Best Lightweight Water Bottle: Platypus DuoLock SoftBottle

Best Filtered Water Bottle: LifeStraw Peak Series

Best Value Backpacking Water Filter: Sawyer Squeeze

Best Survival Water Filter: MSR Guardian

Best Overall Hydration Bladder: CamelBak Fusion

Supplement with Electrolytes

When you sweat and work out, your body loses water and electrolytes. Electrolytes like potassium and sodium carry electronic signals to your cells and are invaluable to your nerves and muscles. Replenishing your electrolytes is crucial to rehydration because they help your body make the most of your water. There are a ton of sports drinks, powders, gels, and fluids centered around electrolytes that you might consider bringing on your hike. 

Read Next: The Best Hydration Bladders of 2023


Q: Is it bad to not drink water all day?

Even mild dehydration can affect your mental and physical performance. If you have a headache or feel tired or dizzy, you should try drinking water. Those who don’t drink enough water every day are at a higher risk of kidney stones, heart issues, and some kinds of cancer.

Q: What happens to your body if you don’t drink water?

Your body will try to conserve water for you if it isn’t receiving enough. This sounds helpful, but it is detrimental to your physical health. You can’t digest food, pass waste, or cool off through sweating efficiently. After these functions start to fail, so will the rest of your body.

Q: Can you survive 7 days with just water?

Likely, yes. Barring any exceptions like a health condition, most people can survive three weeks without food and only water. 

Final Thoughts

The average person can last three days without water, but when you’re exercising or it’s hot outside, that number can drop to just hours. Getting dehydrated in the wilderness often leads to bad decision making and can get you into serious trouble. Drink water regularly while working, exercising, or recreating outside so that you never have to find out: how long can you survive without water?

The post How Long Can You Survive Without Water? appeared first on Outdoor Life.

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