Dehydration is the loss of water and salts from your body. Most people experience mild dehydration at some time, but if it becomes severe it can lead to death.
Feeling thirsty is a sign you need more fluid. Mild dehydration can be treated by drinking small amounts of water frequently. Babies, older adults and people who work outside are most at risk of severe dehydration. Severe dehydration can be a serious problem – seek urgent medical help or call Healthline 0800 611 116.
On this page, you can find the following information:
|If you have a child under the age of 6 months who is vomiting (being sick) or has diarrhoea (runny poos), or you think they might be dehydrated, take them to a doctor right away.
|Read more about dehydration in babies and children.
What are the symptoms of dehydration?
For healthy people, the best way to know that you need more fluid is if you feel thirsty.
In the early stages of dehydration (mild dehydration), symptoms include:
- a dry, sticky mouth and tongue
- feeling lightheaded or dizzy
- a headache
- feeling very tired – no energy.
As dehydration becomes worse (moderate or severe dehydration), symptoms include:
- extreme thirst
- dry mouth and cracked lips
- urinating (peeing) less
- not peeing for 8 hours (a sign of severe dehydration)
- dizziness when you stand up that doesn't go away after a few seconds
- feeling sleepy, tired or confused
- cramping in your arms and legs.
|If you have signs of moderate or severe dehydration, see your doctor or an after-hours clinic immediately or call 111 for an ambulance.
What causes dehydration?
Dehydration is when you don't have enough body fluids for your body to carry out normal functions easily. About 75% (three-quarters) of your body is water. Your bones are 22% water and your blood is nearly all (92%) water. Your body uses water to replace blood and other fluids so it can function properly.
Along with water, your body also needs electrolytes. These are salts normally found in blood, other fluids and cells. When you are dehydrated, you also lose these salts.
You can survive without food for more than 30 days, but less than a week without water.
|Common causes of dehydration
- Diarrhoea (runny poos) and vomiting (being sick).
- Having a fever (high temperature).
- Not eating or drinking while you’re sick.
- Being outside in very hot conditions.
- Not drinking enough before, during or after hard exercise or heavy work.
- Some health conditions such as kidney disease or diabetes – these cause you to urinate (pee) more often.
- Some medicines such as water pills (diuretics) – these can cause your body to lose water.
- Even having a cold or sore throat – 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 under 1-year-old, older adults and people who work or exercise outside.
Babies under 1 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.
As you age, your body's fluid reserve becomes smaller, your ability to retain water is reduced and your sense of thirst becomes less reliable. This is made worse by conditions such as diabetes and dementia, and by certain medicines. Older adults also may have mobility problems that limit their ability to get water easily.
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. This can lead to a higher body temperature and the need for more fluids. Read more about heat stroke and heat exhaustion.
How can I prevent dehydration?
- Always drink plenty of fluids during the day, especially when working or exercising in the sun.
- Where possible, try to do all physical outdoor activities in the 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.
- Water is best. Avoid high-sugar, high-calorie drinks such as undiluted fruit juice, fizzy drinks and sports drinks. They are not as hydrating and drinking these regularly is a leading cause of obesity.
- Avoid caffeinated and alcoholic drinks. These can make dehydration worse as they make you pee more.
What is the treatment for dehydration?
Mild dehydration can be treated by drinking water frequently in small amounts until you are no longer thirsty and your urine (pee) is a light yellow colour. Even if you are vomiting, some of this water will still be absorbed by your body.
If drinking water is not enough to treat the dehydration, your doctor or pharmacist may recommend electrolyte solutions such as Electral or Pedialyte. You can buy these from your pharmacist. Prepare them according to the instructions on the packet. Read more about oral rehydration solutions.
Moderate or severe dehydration often needs treatment in hospital and may involve fluids being given by a nasogastric tube (a tube through your nose into your stomach) or intravenously (through a needle into a vein).
How much water should I drink every day?
How much water you need depends on many factors, including your health, 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. A good guide is the colour of your urine (pee). It 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).
5 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.
- Replace other drinks with water, especially drinks with sugar, caffeine or alcohol in them.
- In winter, drink warm water with lemon, honey or mint leaves.
Read more about drinking the right amount of water.
Dehydration NHS, UK
Dehydration MedlinePlus, US
||Dr Alice Miller trained as a GP in the UK and has been working in New Zealand since 2013. She has undertaken extra study in diabetes, sexual and reproductive healthcare, and skin cancer medicine. Alice has a special interest in preventative health and self-care, which she is building on by studying for the Diploma of Public Health with the University of Otago in Wellington.
Dehydration in children and babies
In children and babies, dehydration is often due to vomiting (being sick) and diarrhoea (runny poos). The younger the child, the easier it is for them to become dehydrated. This is because their bodies are smaller and they have smaller fluid reserves.
If you have a child under the age of 6 months who is vomiting (being sick) or has diarrhoea (runny poos), or you think they might be dehydrated, take them to a doctor right away.
Also, if your child of any age has the following signs, see your doctor or go to an after-hours clinic immediately or call 111 for an ambulance:
- dry mouth, lips and tongue
- fewer wet nappies than usual or dark-coloured urine (pee)
- no tears when crying or sunken eyes
- cold hands and feet
- mottled bluish skin
- unusual lack of energy, sleepiness or difficult to wake.
How can I prevent dehydration in my baby or child?
Dehydration due to vomiting and diarrhoea can be prevented by giving your child fluids. Whichever fluids your child is having, the important thing is to:
- offer small amounts of fluid often rather than giving large amounts
- aim for quarter of a cup every 15 minutes or 1 teaspoon or 5 mls in a syringe every minute
- keep offering your child fluids even if they are vomiting.
What fluids should I give my baby or child to avoid dehydration?
- If you are breastfeeding, continue to feed on demand. You may need to increase the frequency of feeds and give extra fluid.
- If your child is on formula, continue to give them formula feeds.
- If your child is over 1 year, you may give them cow’s milk.
- Water is generally the best fluid.
- Offer small amounts of fluid often rather than giving large amounts.
- Aim for ¼ of a cup every 15 minutes or 1 teaspoon or 5 mls in a syringe every minute.
- Keep offering your child fluids even if they are vomiting.
- If your child vomits, wait 5 to 10 minutes and then start giving fluid again, but more slowly ( eg, a spoonful every 2 to 3 minutes).
You may also give your child the following drinks as long as they are not dehydrated. These drinks MUST be diluted with water as they contain too much sugar (which can make diarrhoea worse):
- cordial – make up to normal drinking strength then add 5 parts of water to 1 part of the diluted cordial
- soup – add 5 parts of water to 1 part of soup
- fruit juice – add 5 parts of water to 1 part of juice.
Your doctor or pharmacist may recommend electrolyte solutions such as Electral or Pedialyte if your child is mildly dehydrated. You can buy these from your pharmacist. Prepare them according to the instructions on the packet. Read more about oral rehydration solutions.
Don’t give your child these drinks
Do not give your child undiluted fizzy drinks, fruit juices, Lucozade, Ribena or sports drinks (such as Powerade or Gatorade). These contain too much sugar and can make your child’s diarrhoea worse.
Also, don’t give them coffee and tea as these can make your child become dehydrated.
Information for healthcare providers on dehydration
The content on this page will be of most use to clinicians, such as nurses, doctors, pharmacists, specialists and other healthcare providers.
Assessment of dehydration in children
From Gastroenteritis Starship Clinical Guideline, NZ, 2017:
- The best way to find out is to measure weight loss, but a recent weight is seldom available. Clinical estimate of the degree of dehydration is unreliable. Doctors usually overestimate the deficit, and may underestimate it if there is hypernatraemia.
- In the management of dehydration, it is much more important to follow a child closely over time, than it is to calculate and replace a hypothetical figure for % dehydration.
- Slightly dry buccal mucosa
- Dry buccal mucosa, absent tears
- Sunken eyes & fontanelle
- Decreased urine output
- Altered skin elasticity
- Signs of ketosis (rapid shallow breathing, smell of ketones)
- Shock (tachycardia, poor volume peripheral pulses, cool peripheries)
- Hypotension is late/ominous sign
- Skin retraction time > 2 seconds
- Capillary refill time > 3 seconds
|As a rough guide, the child who is mildly dehydrated (≈5%) may be considered to have a 50 ml/kg deficit, and the child who is shocked (≈10 - 15%) may be considered to have at least a 100 ml/kg deficit.
Oral rehydration therapy (ORT) for children
This is the treatment of choice for dehydration from gastroenteritis. It is safer and more effective than IV therapy for all degrees of dehydration except shock. ORT uses Oral Rehydration Solution, which takes advantage of glucose/sodium co-transport mechanisms in the small bowel.
Certain principles must be remembered:
- ORT is intensive. It depends on a lot of input from the child's caregiver, or the use of a nasogastric tube.
- Pedialyte is the ORS of choice.
- The treatment of gastroenteritis with ORS occurs in two phases: rehydration and maintenance. Except in hypernatraemia, ORT aims for full rehydration within 4 hours.
- The schedule suggested here for the rehydration phase is a standard rate of replacement for all dehydrated children who are not shocked, over 4 hours. The final volume given is determined by clinical assessment of when the child is rehydrated.
- During the rehydration phase, fluid is given at a rate of 5 ml per minute, by teaspoon or syringe. The small volumes decrease the risk of vomiting. The rate (1 teaspoon / minute) is easy to calculate and administer for a parent sitting at the bedside. 25 ml every 5 minutes can also be used. If oral rehydration not successful, then naso-gastric rehydration should be used.
- This rate of replacement is already maximal, and is not supplemented for ongoing losses. If the child's ongoing losses exceed an intake at this rate, the child will require nasogastric or intravenous fluids. This rate will rehydrate a moderately dehydrated 1 year old in 2 to 4 hours and a 2 year old in 3 to 5 hours (estimating diarrhoea at 0 -10 ml per kg per hour).
- An alternative rate is 25 ml / kg /hr, over 4 hours, in small aliquots frequently.
- There must be frequent review (at least 2 hourly) in the rehydration phase.
- Vomiting is not a contra-indication. Most children with gastroenteritis who vomit, will still absorb a significant percentage of any fluid given by mouth or NG.
- Half strength apple juice has been shown to be a suitable alternative for children with mild gastroenteritis and minimal dehydration.
Gastroenteritis Starship Clinical Guideline, NZ, 2017
Oral rehydration therapy (ORT) NZ Formulary for Children
Diarrhoea and vomiting caused by gastroenteritis in under 5s: diagnosis and management NICE Guideline, 2009
Assessment and management of infectious gastroenteritis BPAC, NZ, 2009
Regional HealthPathways NZ
Access to the following regional pathways is localised for each region and access is limited to health providers. If you do not know the login details, contact your DHB or PHO for more information: