Dehydration is the loss of water and salts from the body.

Dehydration is the loss of water and salts from the body. When you are dehydrated, you do not have enough body fluids for your body to carry out normal functions easily. Severe dehydration can be a serious problem, leading to collapse and even death.

Most people will experience some degree of dehydration at some point during their life, but the condition is especially dangerous for babies and young children and older adults.

Tips: ways to avoid dehydration:

  • Always drink plenty of fluids during the day, especially when working or exercising in the sun.
  • Where possible, try to schedule all physical outdoor activities for cooler parts of the day.
  • Drink water before you play sport, during if possible, and after to ensure your body stays hydrated. 
  • Drink plenty of fluids if you have diarrhoea, vomiting or fever – see your doctor if you cannot keep fluids down.

Why does the body need water?

The human body needs water to replenish the blood and other fluids in order to function properly. About 75% of the human body is water; our bones are 22% water and our blood is 92% water. Along with water, the body also needs electrolytes. These are salts normally found in blood, other fluids and cells.
People can survive without food for more than 30 days, but less than a week without water.

What causes dehydration?

The common causes of dehydration are:

  • diarrhoea and vomiting
  • having a fever and not eating or drinking while ill
  • being outside in very hot conditions
  • not drinking enough before, during or after strenuous exercise or hard work
  • some medical conditions such as kidney disease or diabetes cause you to urinate (pee) more often and certain medicines can cause the body to lose water such as water pills (diuretics)
  • even having a cold or sore throat makes you more susceptible to dehydration because you're less likely to feel like eating or drinking when you're sick.

Who is at risk of dehydration?

Although anyone can become dehydrated, those who become dehydrated most easily are:

  • Babies under1 year old
    • Dehydration can quickly become serious in children. If you have a child under the age of 6 months who has vomiting/ diarrhoea, or whom you suspect is dehydrated, take them to see a doctor right away. Young children often can't tell you that they're thirsty, nor can they get a drink for themselves. The younger the child, the easier it is for them to become dehydrated. Read more about dehydration in babies and children.
  • Older adults
    • As we age, our body's fluid reserve becomes smaller, our ability to retain water is reduced and our sense of thirst becomes less reliable. These problems are made worse by illnesses such as diabetes and dementia, and by the use of certain medications. Older adults also may have mobility problems that limit their ability to obtain water for themselves.
  • People who work or exercise outside.
    • When it's hot and humid, your risk of dehydration and heat illness increases. That's because when the air is humid, sweat can't evaporate and cool you as quickly as it normally does, and this can lead to an increased body temperature and the need for more fluids.

What are the symptoms of dehydration?

For healthy people under normal circumstances, thirst is a reliable indication of our bodies need for more fluid.

In the early stages of dehydration (mild dehydration):

  • dry, sticky mouth and tongue
  • feeling light headed or dizzy
  • weakness and headache
  • feeling very tired – no energy.

As dehydration becomes worse (moderate dehydration)

If you have these signs, visit your doctor or an after hours clinic immediately or call 111 for an ambulance.
  • extreme thirst, dry mouth, cracked lips
  • urinate (pee) less - not passing urine for 8 hours
  • dizziness when you stand up and it doesn't go away after a few seconds
  • weakness, sleepy and tired
  • cramping in the arms and legs.

How to prevent dehydration?

To prevent dehydration make sure you drink enough fluids. Thirst is a good guide to when fluids need to be replaced and water is generally the best choice.

  • Diluted fruit juice (1 part juice to 10 parts water) is an acceptable alternative, but it’s best to avoid high-sugar, high-calorie drinks such as undiluted fruit juice and fizzy drinks.
  • Also be wary of sports drinks as they often contain a lot of sugar and additives.
  • High-sugar, high-calorie drinks are not as hydrating as water. Plus, drinking these regularly is a leading cause of obesity, which greatly increases your risk of developing Type 2 Diabetes. Diabetes is the biggest cause of kidney failure in New Zealand and the New Zealand Kidney Foundation strongly advises water as an alternative.
  • Also avoid caffeinated and alcoholic beverages as these can make dehydration worse, as they increase urine output.

How much water should I drink every day?

Just as you are unique, so are your water needs. How much water you need depends on many factors, including your health status, how active you are and where you live.

It has been recommended we should drink 6 to 8 glasses of water a day. This is a good guide, although there is no research-based evidence to support this. Perhaps a better recommendation is to use the colour of your urine as a guide to how much water you should be drinking. Your urine should be a very light-coloured yellow. If it is a deep yellow then it is likely you are not drinking enough water.

If you have kidney stones, drinking plenty of water each day can lower your chances of getting another stone. You should also drink extra amounts of water when experiencing any dehydrating conditions (such as hot, humid weather, high altitudes or physical exertion).

Easy ways to drink more water

  • Carry a water bottle with you.
  • Set an alarm or download an app to remind you when to drink more fluids.
  • Have a glass of water before and after each meal — a lemon, lime, orange, or your favourite fruit to keep your taste buds satisfied.
  • In winter, drink warm water with lemon, honey or mint leaves.

Learn more

Dehydration NHS choices

Dehydration MedlinePlus (US), Aug 2013

Credits: New Zealand Kidney Foundation. Updated by Health Navigator, August 2014.