Water is the largest single component of the human body, including your brain, and it is essential for life. Generally speaking, people can only survive about a week without water. However, a lot depends on the weather conditions, your level of body fat and your general health status. Being in hot climates, being obese or sick can reduce the amount of time you can survive without water.
Length of Time
Humans cannot survive without water. Because your body can't store it, you must replace the fluid you lose on a daily basis. You need water and other fluids to support functions such as excretion of waste materials and evaporation from your lungs and skin. The U.S. Geological Survey estimates that the average human can survive only a week without water. But exact recommendations about how much water you need are based on a number of other conditions.
Temperature, humidity level and altitude are some factors that can play into how long you can survive without water. For example, hot and humid conditions can make you sweat more, creating fluid loss that requires you to take in additional fluids to keep your body functioning optimally. In addition, being higher than 8,200 feet often results in more frequent urination and faster breathing, which uses up more of your body water.
Age, Body Fat and Gender
How long you can survive without water also depends on how much total body water content you have. Total body water varies by age, gender and body fat. Men's bodies are composed of about 60 percent water, and women's bodies are composed of about 55 percent. Babies' bodies are composed of about 78 percent water. The higher your body fat, the less the percentage of fluid you have. The less body water you have, the less time you can survive without water.
General Health Status
Illness, such as fever, diarrhea and vomiting, can cause you to lose additional fluids. In addition, taking certain medications -- especially diuretics -- can also exacerbate fluid loss. Being sick can limit the amount of time your body can function properly without replacing lost fluids. On the other hand, engaging in a great deal of physical activity or exercise, even walking long distances because of famine, can increase the amount of water you need to survive.
Water Intake Recommendations
The Institute of Medicine states that most adult men need about 3.7 liters of water daily and women 2.7 liters. Water is best, but you can meet some of your water intake needs through other kinds of fluids as well as foods that have a high moisture content. Toddlers up to age 3 years, need about 1.3 liters daily, and between ages 4 and 8, roughly 1.7 liters is considered adequate intake. Boys between the ages of 9 and 18 need between 2.4 and 3.3 liters daily; girls in that age range need between 2.1 and 2.3 liters. Pregnant and nursing moms need 3 and 3.8 liters, respectively.