• We become dehydrated if our bodies do not have enough water. This can happen through a combination of causes, such as not drinking enough water or fluids, or losing too much body fluid (for example through sickness or diarrhea)

  • Dehydration is usually described as mild, moderate, or severe, according to how much body weight has been lost due to fluid loss

  • Mild dehydration is the loss of 3-5% of your body weight. It carries few risks can usually be dealt with by replacing lost salts and fluids

  • Moderate dehydration is a loss of between 5-9% of body weight and is rather more serious. Moderate dehydration that is chronic (ongoing) can affect kidney function and may lead to the development of kidney stones. This can also be dealt with by replacing lost salts and fluids

  • Severe dehydration (a decrease of more than 10% of body weight due to fluid loss) is very serious and needs immediate treatment as it can be fatal. You may need to go to hospital and be put on a drip to restore lost fluids

  • Dehydration can be very serious in children and babies because they have a low body weight, making them even more susceptible to fluid loss


Dehydration happens when we lose more fluid than we take in. We lose body fluid and salt throughout the day in sweat, tears, urine and stools (feces). Usually, the water and salt content of what we eat and drink make up this loss – but we become dehydrated if fluid loss exceeds fluid intake.

Our kidneys and intestines work together to control the level of fluid in the body. The intestines absorb salt and water, while the kidneys regulate how much of this is lost through urine. If a large amount of fluid is lost through diarrhea, then the kidneys may be unable to regulate the balance of salt and water. This means that you may need extra salt as well as extra water.