Water is vital to human life—so much so that we can’t go more than a few days without it. About 60% of your body is made up of water. On average, men need to drink about 3 liters—more than three-quarters of a gallon—of fluids every day to stay fully hydrated. Women need about 2.2 liters—more than half a gallon—of fluids a day. (The water in foods also counts toward that total fluid intake.) When your body gets less water than it needs, you may start noticing early dehydration effects, such as dry mouth, extreme thirst, infrequent urination, or dark urine. With severe dehydration, however, the symptoms can become dangerous and even life threatening.

Water serves many purposes in the body, and without enough fluids, your body can’t function correctly. Among the many things water does in the body:

• Regulates body temperature through sweating
• Provides fluid to blood and lymphatic vessels
• Removes waste
• Transports nutrients to every cell through the bloodstream
• Cushions the brain and spinal cord and lubricates joints
• Creates saliva

Without water, many problems—sometimes extremely serious ones—can develop in the body. Mild dehydration can typically be treated just by drinking more water, but moderate and severe dehydration aren’t so easily treated and can pose a danger to your health. Severe dehydration is a life-threatening emergency and requires  immediate treatment by a medical professional. The most serious dangers of dehydration include:

• Hypovolemic shock: This condition is also known as low blood volume shock. The link between dehydration and blood pressure can be a life-threatening situation. If you become dehydrated, your blood volume can plunge, which can cause a drop in blood pressure and too little oxygen in the blood. Your heart won’t be able to pump enough blood, which can cause your organs to fail. Treating hypovolemic shock is an emergency and requires an intravenous (IV) line to restore fluids and administer medication.
• Kidney problems: Dehydration can cause waste to build up in the body because there isn’t enough water to deliver the waste to the kidneys. This also can cause muscle proteins to clog the kidneys, which can lead to kidney stones and urinary tract infections. Frequent or chronic dehydration symptoms can lead to permanent kidney damage.
• Seizures: Dehydration from vomiting, diarrhea, or excessive sweating causes an imbalance of the electrolytes in the body. This electrolyte imbalance can affect the brain’s function and metabolism, which can lead to seizures.
• Heat illnesses: Without drinking enough water on a hot day or while doing strenuous exercise, the extra sweating can dehydrate you. You also could suffer heat injuries, such as heat cramps, heat exhaustion or heatstroke. When you’re dehydrated, you may become unable to sweat enough to lower your body temperature, and your body overheats. Heatstroke can happen quickly and is a life-threatening emergency.

If you’ve been experiencing diarrhea or vomiting, you have a high risk of becoming dehydrated. Not drinking enough water on a hot day or while exercising, or even just a high fever, can cause dehydration. Young children and elderly people are most likely to experience dehydration. It’s especially important to watch for symptoms of dehydration in babies because they can’t tell you they’re thirsty. Symptoms of dehydration in babies include:

• No tears when crying
• Sunken soft spot on the head
• Sunken eyes
• No wet diapers in three or more hours

To prevent dehydration, make sure babies are drinking enough breast milk or other fluids, especially if they have diarrhea. In general, infants up to 6 months old getting adequate fluids should gain 5 to 7 ounces a week and infants 6 to 12 months about 4 ounces a week. Although infant weight gain is variable, weight loss or no weight gain may be a sign of dehydration and requires prompt medical evaluation.

In adults, good prevention methods include making sure other health conditions, such as diabetes, are under control and eating foods with high water content, like fruits and veggies. And everyone should be drinking plenty of fluids when out in hot weather and when exercising.