By , July 26th 2013. Last reviewed 29th April 2016.

What is a medical definition of dehydration?

Dehydration [from Latin de- = removal; Greek hydros = water] is a lack of water in the body that results in at least 1% loss of body weight [1,2]; a smaller loss is considered a normal fluctuation of the body water.

Synonyms  for dehydration are hypohydration and water deficiency.

What does dehydration mean in lay terms?

Dehydration literally means “dryness of the body.” When you are dehydrated, your body does not have enough water to function properly [2,3].

Anyone can get dehydrated in summer, winter or at any time.

Why do we need water?

Most biochemical processes in the human body take place in water. Water is also needed for the blood flow, excretion of waste substances with the urine, lubrication of the gastrointestinal and respiratory tract and sweating.

Body Water Percentage

Average water percent in humans [4]:

  • Newborns and infants up to 6 months: ~75% (range: 64-84%)
  • Infants older than 7 months and children up to 12 years: ~60% (range: 50-75%)
  • Males older than 12 years: ~60% (range: 43-73%; more in lean athletes, less in obese individuals)
  • Females older than 12 years: ~50% (range: 40-60%)

Acute and Chronic Dehydration

Acute dehydration last less than a day and chronic dehydration more than a day.

Symptoms and Signs

  • Mild dehydration: thirst, dry mouth, pale yellow urine (check urine color chart), slightly prolonged skin turgor (up to ~3 seconds) and 1-2% loss of body weight.
  • Moderate dehydration: dry lips, tiredness, yellow urine, prolonged skin turgor (several seconds) and 3-6% loss of body weight.
  • Severe dehydration: severe thirst, fatigue and headache, brown urine and loss of more than 6% of body weight.


You can get dehydrated by not consuming enough water or by losing water from your body.

The main causes of dehydration:

Diagnosis and Treatment

A doctor can make a diagnosis of dehydration from symptoms, signs, skin turgor test and blood and urine tests.

Treatment of mild and moderate dehydration is by drinking water and of severe dehydration by an infusion of the fluids into a vein.


When you do not treat severe dehydration promptly, you may suffer from serious complications, such as seizures, hypovolemic shock, heat stroke, acute kidney failure or blood clots or you can die.

How long can you survive without water?

  • People have survived without water and food for up to 8 days.
  • In a hot environment (desert) you may survive only for one day without water.

Related articles: