The general consensus is that people can survive for around three days without water, with estimates typically ranging from two days to a week. Wilderness guides often refer to the “rule of 3”, which says that a person can live for 3 minutes without air (oxygen), 3 days without water, and 3 weeks without food.
Nutrition Reviews, a peer-reviewed international journal that focuses on literature reviews about nutrition-related topics, published two articles in 2010 that mention how long people can go without water. Authors of one article state “only for days”, while the other states 2-4 days. Without water, a person can die after 3 days, and usually no one can survive for more than 5-6 days. Dr. Claude Piantadosi of North Carolina’s Duke University says 100 hours is around the limit.
The world record for the longest survival time without water and food is 18 days, achieved by an 18-year-old man in Austria who was accidentally locked in a government facility in 1979. He was in a near-death state when he was discovered.
These numbers only serve as a guide. Many different factors affect the length of time someone can survive without water, including the environment, level of activity, age, health status, and other unique individual characteristics.
While food contains some water, the amount depends on the type of food, surviving without water generally refers to not drinking water or other beverages.
Why Does The Period Of Time That You Can Live Without Water Vary?
The period of time that you can live without water varies because of environmental factors, activity level, age, health status, weight, gender, and food intake. These main factors are broken down as follows.
- Environment: Environmental factors can affect the period of time that you can live without water.
- Temperature: According to Dr. Piantadosi, “Depending on the temperature you are exposed to, you can go 100 hours without drinking at an average temperature outdoors. If it’s cooler, you can go a little longer. If you are exposed to direct sunlight, it’s less.” During hot weather, people of any age are at risk for dehydration.
- Humidity: In humid weather, sweat does not evaporate from the body as quickly, meaning the body can’t release heat via sweat as effectively. This leads to increased body temperature, which can lead to heatstroke. According to the Mayo Clinic, heatstroke can result in loss of consciousness, seizures, and death if untreated, as outlined in the infographic below from the Texas Military Department.
- Activity level: The body uses less water at rest and more water during exercise. An increase in exercise intensity or duration leads to increased body heat production and increased sweating rate, both of which contribute to dehydration.
- Age: Older adults have less water in their bodies, so they are more sensitive to water loss, such as from illness or medication side effects. Additionally, according to a book published by the Institute of Medicine in 1993 titled “Water Requirements During Exercise in the Heat”, older adults are more intolerant of heat due to a decrease in sweating capacity or aerobic fitness, or both. However, young children, as well as older adults, are in greater danger during dehydration compared to other age groups.
- Health status: According to the Mayo Clinic, dehydration in young children is most commonly due to severe vomiting and diarrhea. Vomiting and diarrhea can also lead to faster dehydration in people of all ages. People running a fever or experiencing frequent urination, such as from uncontrolled diabetes, are also at greater risk.
- Weight: According to the Centers for Disease Control and Prevention (CDC), overweight people are among those with the greatest risk during a heat-related illness. Elevated heat levels in the body are caused by a lack of water. Additionally, according to the Cleveland Clinic, people who weigh more generally need more water. To find out roughly how much water you should consume per day, this diagram gives an easy rough formula.
- Gender: According to the U.S. National Academies of Sciences, Engineering, and Medicine, women should drink 2.7 liters of fluid per day, while men should drink 3.7 liters of fluid per day (may vary depending on the other factors listed here). However, women need more water during pregnancy and breastfeeding.
- Food intake: Food contributes to overall water intake. In fact, the Mayo Clinic and Cleveland Clinic both note that roughly 20% of fluid intake per day comes from food. Eating foods high in water content such as cucumbers, celery, iceberg lettuce, watermelon, and strawberries will affect a person’s hydration status and therefore how long they can survive without directly drinking fluids.
What Can Help Improve The Chance Of Surviving Without Drinking Water?
Your chance of surviving without drinking water is improved by decreasing activity, regulating temperature, choosing ideal travel times, eating certain foods, avoiding certain medications, and strengthening your immune system:
- Minimize activity level: Avoid spending more energy than necessary, and avoid excessive sweating. Both will help the body to lose water.
- Regulate body temperature: Stay in an environment with a comfortable temperature. Keep warm when it’s cold, and cool off or seek shade when it’s hot. This involves wearing the correct clothing for the weather.
- Travel smart: Anticipate your next move. If you know you’ll be traveling the next day, set off in the early morning when it’s cooler outside.
- Eat foods high in water content: If possible, eat foods that are easy to digest with high water content to support your overall fluid intake.
- Avoid certain medications: Diuretic medications, also called “water pills”, should be avoided if possible, as they increase urination. Other medications that can increase urination include certain sleeping pills, antidepressants, and medications that treat high blood pressure.
- Strengthen your immune system: If you are trying to increase your chances of surviving without water in the future, it doesn’t hurt to strengthen your immune system to help decrease the risk of illness and disease. Diarrhea and vomiting from disease can quickly deplete your body water in critical times. The figure below displays a number of ways you can support and strengthen your immune system.
What Can Help Decrease The Chance Of Surviving Without Drinking Water?
Your chance of surviving without drinking water is decreased by drinking alcohol, using too much energy, eating too much food, eating snow, drinking seawater, or remaining at a high altitude. To expand upon these points:
- Drinking alcohol: Alcohol causes increased urination, which can promote dehydration.
- Expending too much energy: The more energy you spend, the more water you’ll need to replenish the water used up.
- Eating too much food: John Wiseman, a survival expert and member of the United Kingdom’s Special Air Service (SAS), states in his book “SAS Survival Handbook” that a person should not eat or eat as little as possible if water is unavailable. This is because the body uses water to digest food, and this can worsen dehydration.
- Eating snow: The Institute of Medicine’s book “Nutritional Needs in Cold and In High-Altitude Environments” published in 1996 notes that converting snow into water for drinking is an impractical use of time and energy for military operations. Additionally, survival prepping guides note that eating snow can promote dehydration by lowering the core body temperature and using body energy and water to convert snow into water.
- Drinking seawater: According to the US National Ocean Service, seawater has a high salt content that humans aren’t able to process, leading to more thirst and dehydration.
- Staying at a high altitude: As noted by the Wilderness Medical Society and Mayo Clinic, dehydration can happen more easily at higher altitudes. High altitudes are associated with increased urination and faster breathing and sweating rates because of dryer climate, leading to greater fluid loss.
When Does A Person First Feel Thirsty After Stopping Drinking Water?
A person first feels thirsty after stopping drinking water when the concentration of electrolytes in their blood rises 2-3%. This measure of electrolyte concentration is called plasma osmolality and the receptors that sense changes in it are located in the part of the brain called the anteroventral hypothalamus.
The Merriam-Webster dictionary defines thirst as “a desire or need to drink”, and also “the bodily condition (as of dehydration) that induces this sensation”. This shows us the simpler answer to the question of when we feel thirsty: when the body doesn’t have enough water, we feel thirsty. The conditions that can lead to the body having insufficient water are nearly endless, but the body is extremely good at signaling this to us through thirst.
As noted by Unicef, thirst is one of the first signs of dehydration. Dr. Irvin Sulapas, a primary care physician and professor at Baylor College of Medicine in Texas, states that “The rule of thumb is, if you’re thirsty, you’re already dehydrated.”
Does Water In Food Help When Drinking Water Is Restricted?
Yes, eating food high in water content that is easily digestible helps with overall fluid intake when drinking water is restricted. According to Wiseman, digesting fat is the hardest and requires a lot of water. The Federal Emergency Management Agency (FEMA) recommends not eating salty foods as they can increase thirst.
Foods high in water content include cucumbers (95% water), celery (95%), iceberg lettuce (95%), tomatoes (95%), zucchini (nearly 95%), spinach (93%), cauliflower (92%), watermelon (91%), yellow melon (e.g. honeydew, 91%), strawberries (91%), and cantaloupe (90%).
What Body Functions Are Most Affected By Not Drinking Water?
Body functions that are most affected by not drinking water include the following processes.
- Cognitive performance: Dehydration can cause confusion, dizziness, and worsened ability to focus and think clearly.
- Mood: Dehydration can cause restlessness, agitation, tiredness, and possibly mood swings caused by changes in dopamine levels.
- Physical function: Dehydration can cause weakness and decreased physical performance.
- Waste elimination: Dehydration can cause dark-colored urine, less urine volume, and constipation.
- Heart and lung function: Dehydration can cause fast heart rate, low blood pressure, and fast breathing.
- Temperature regulation: Dehydration can cause fever.
- Digestion: Dehydration weakens the body’s ability to form saliva.
- Joints: Dehydration weakens the body’s ability to lubricate the joints.
- Cell function: Dehydration weakens the body’s systems for cell growth, reproduction, and survival.
What Are The Risks Of Water Intake Restriction (Dehydration)?
The risks associated with water intake restriction (dehydration) include cognitive impairment and decreased productivity.
- Impaired cognitive ability. A study conducted by Gopinathan et al. found that mental function decreased significantly when 2% or more of body weight was lost due to dehydration. Impaired functions included short-term memory, visual tracking, attention, and arithmetic ability.
- Decreased work productivity. A review paper titled “Hydration at the Work Site” written by PhDs Robert Kenefick and Michael Sawka from the US Army Research Institute of Environmental Medicine in Massachusetts noted that dehydration can negatively impact worker productivity. The graph below is taken from this study and shows that subjects’ reaction times were found to increase with worsening dehydration. Another study conducted by Wasterlund and Chaseling titled “The Effect of Fluid Consumption on the Forest Workers' Performance Strategy” studied the effect of decreased water intake on forest workers’ productivity and found a 12% reduction.
Dehydration is defined as losing more fluid than the amount of fluid taken in without a proportional decrease in sodium and potassium levels. Studies have shown that dehydration results in a decrease in mental ability and work productivity.
How Does The Percentage Of Water In The Body Affect Lifespan?
The percentage of water in the body can affect one’s lifespan detrimentally if it gets too low, with an 8% loss or more potentially fatal. What Percentage of the Human Body is Water? A person’s age will affect their body water composition. Water makes up about 75% of body weight in infants, 70% in a normal adult, and only 50% in older adults. This means that older adults are more sensitive to changes in body water.
People with less fat tissue tend to have a greater percentage of body water than people with more fat tissue. Men generally have a greater percentage of body water than women, as women have a greater percentage of body fat, as displayed in the chart below.
According to BioMed Central (BMC) Public Health, a loss of 1-2% of body weight due to water is associated with decreased cognition; 4% loss is associated with decreased performance, headaches, tiredness, and irritability; and 8% loss or more is fatal.
What Precautions are Helpful For A Person Whose Access To Water Is Restricted While Out In Nature?
Precautions that can help people whose access to water is restricted while out in nature include avoiding searching in places where water does not naturally collect, avoiding water pools with no green vegetation, and not trying to ration water over a long period of time.
When looking for sources of water in nature, survival expert John Wiseman recommends first looking in valleys where water will naturally collect. Even if no source of water is easily spotted, you can try digging in areas of vegetation, or dry beds where streams used to be. Water may be found in crevices in the mountains, under sand dunes by the beach, or near vegetation on cliffs. In the event these options are exhausted, Jonathan Strickland of the popular BrainStuff YouTube channel describes alternative ways one may be able to retrieve water in the wilderness.
John Wiseman also provides a helpful hint. Be wary of pools without green vegetation (may contain toxic chemicals), and in pools without outlets, be sure to distill the water before drinking. Wiseman emphasizes water from pools must always be boiled before drinking.
FEMA recommends drinking the amount needed for each day instead of rationing the supply over a longer period of time if you have a limited supply of water. The goal should be to find more water, if possible, after drinking the amount you need.
The average amount of fluid intake should be close to 1.5 liters/day, according to the British Medical Journal (BMJ). The BMJ also recommends supplementing water with 1.5 grams of sodium chloride per day, or about half a teaspoon of table salt. Too much sodium chloride can cause low potassium levels.
How Does Water Intoxication (Drinking Too Much Water) Affect Lifespan?
Water intoxication happens when too much water is consumed, leading to decreased concentration of sodium in the body (hyponatremia). The normal level of sodium in the blood is around 135-145 milliequivalents per liter or mEq/L. During hyponatremia, the level is lower.
Unlike water restriction, excess water leads to a different set of problems. Hyponatremia symptoms can range from mild to severe. When the sodium level drops quickly, it can cause brain swelling which could be fatal or result in coma. Hyponatremia can also cause seizures, muscle weakness and cramping, confusion, and tiredness.
Neither too little nor too much water is ideal for the body, and it is a good idea to avoid the extremes of both situations.