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What is Dehydration?

Last updated on 21st April 2023

Many people do not realise how prevalent dehydration is in the UK. According to Water Logic, people in the UK are only drinking 53% of their optimal level of water consumption every day.

There are no exact figures of how many people experience dehydration every year in the UK because many mild and moderate cases can be treated at home. However, the International Longevity Centre (ILC) UK reported that a quarter of all care home patients who are admitted to the hospital are dehydrated.

What is dehydration?

Dehydration occurs when your body loses more water and fluid than enters it. When you are dehydrated, your body does not have as much water as it needs and cannot function properly.

The human body is approximately 75% water. A large percentage of water makes up our organs, bones and skin and is also found inside cells and blood vessels. Without this water, humans cannot survive. The body, therefore, works to maintain our water levels and keep them balanced at all times.

Water balance is affected by your water input vs water output. Several factors can influence your water balance, including:

  • Physical activity.
  • Environmental conditions.
  • Diet and food intake.
  • Temperature and weather.
  • Your age.
  • Illnesses and medication.

If you do not properly control how much water is entering and leaving your body, you are likely to experience a water deficit.

Water has an essential role in a number of bodily functions, including:

  • Metabolic processing.
  • Balancing electrolytes.
  • Regulating body temperature.
  • Acting as a lubricant for internal organs and joints.
  • Protecting organs, the spinal cord and joints.
  • Flushing out waste products from the liver and kidneys.
  • Aiding digestion.
  • Helping your brain to function properly.
  • Keeping your cardiovascular system healthy.

Water is constantly lost throughout the day in a variety of ways, including through breathing, sweating, urinating and defecating. It is vital to replenish the water that is lost by drinking more fluids. If your water levels become imbalanced, your thirst mechanism will activate. Thirst is your body’s way of telling you that you need to increase your fluid intake.

If you begin to become dehydrated, your body may begin to move water around to the areas that need it most. However, if you still do not replenish your fluids, your body will not have the fluids it needs to function properly, and you will begin to experience the effects of dehydration.

If you become dehydrated, you need to replace the water and electrolytes that your body has lost. Electrolytes are essential minerals in your body that have an electrical charge, such as sodium, calcium and potassium. They are vital to many of the key functions in your body, including balancing the amount of water in your body, balancing your body’s pH levels, moving nutrients into your cells, moving waste out of your cells, and regulating your blood pressure.

You get electrolytes from the things you drink and eat. If the amount of water in your body changes, your electrolytes can become too low. If your electrolytes become too low, you will likely experience dehydration.

When your water levels are low and you are missing electrolytes, your body will become dehydrated. Depending on how much fluid you are missing from your body, you may experience mild, moderate or severe dehydration.

  • Mild Dehydration – Dehydration can occur if you lose just 1%-2% of your total body weight due to water depletion. Mild dehydration occurs when you lose less than 5% of your total body weight. You are likely to experience some physical symptoms, although you are still likely to be alert and responsive and maintain a normal heart rate, normal blood pressure, breathing and skin colour.
  • Moderate Dehydration – Moderate dehydration occurs when you lose 5%-9% of your total body weight due to water depletion. You are likely to experience more extreme physical symptoms, as well as feeling lethargic and irritable. You may also have an increased respiratory rate, sunken eyes and dry mucous membranes.
  • Severe Dehydration – This is when you lose 10% or more of your total body weight due to water depletion. You are likely to have a reduced conscious state and be experiencing tachycardia – an increased heart rate of above 100 beats per minute. You will likely also experience hypotension, increased respiratory rate, pale skin, cold extremities and a weak pulse.
Woman suffering from mild dehydration

How to reduce the risk of dehydration

There are several things you can do to help reduce the risk of dehydration. This includes:

  • Don’t wait until you are thirsty to drink – This is because thirst is a sign your body is already beginning to feel the effects of dehydration.
  • Always have water at hand throughout the day and night – You are more likely to drink more if you keep water close at hand.
  • Drink a glass of water as soon as you wake up in the morning – This is because spending eight hours without water can mean you wake up already dehydrated.
  • Drink more water in warmer weather – Hotter temperatures and higher humidity can cause you to sweat more and your skin to overheat. You will need to drink more water to account for the fluids you have lost.
  • Don’t skip meals – You can also get some of your fluid intake from food, with approximately 20% of your fluid intake coming from the foods you eat.
  • Eat a balanced diet – Fruits and vegetables contain large amounts of water, salt and vitamins that can help your body to prevent dehydration.
  • Think about what you are drinking – Limit how much high-protein, caffeinated, fizzy and alcoholic beverages you drink as they can dehydrate you.
  • Up your fluid intake when exercising – You will need to drink additional fluids to account for the water that will be lost through sweat and faster breathing. Drink water four hours before you begin any form of exercise and after you have finished exercising. You will also need to drink water during exercise, ideally every 10-15 minutes.
  • Drink more water than usual if you have a high fever, vomiting or diarrhoea – This is because your body will lose more water than usual if you are experiencing any of these symptoms.
  • Check the colour of your urine regularly to keep an eye on your hydration levels – Urine that is clear, or a pale yellow colour, is a sign that you are hydrated. If your urine is a dark yellow or brown colour, this is a sign that your water levels are imbalanced, and you are not properly hydrated.
  • Check how moist the inside of your mouth is – The inside of your mouth, also known as the mucus membrane, should be moist. If it feels dry this can be a sign you are dehydrated.
  • Be aware if you are in a high-risk group for dehydration – Babies, young children and the elderly are at higher risk of dehydration than other groups.

What is the fastest way to cure dehydration?

If you become dehydrated, you need to replace the water and electrolytes that your body has lost. The fastest way to do this is to drink an electrolyte drink. Electrolyte drinks can be in the form of a powder or tablet that you mix with water, or they can be in liquid forms, like a regular drink.

Different electrolyte drinks have different levels of sugar, sodium, potassium, magnesium and calcium. Electrolyte drinks can help to relieve dehydration and can help to replenish hydration after intense exercise, if you are ill, or if you have sweated heavily.

If you are experiencing severe dehydration, drinking an electrolyte drink, or rehydrating with water, may not alleviate your dehydration. You may need to seek medical attention immediately. You may need to go to the hospital and be treated with intravenous (IV) fluids.

Man rehydrating with glass of water

Signs and symptoms of dehydration in adults

An important sign of dehydration that all adults should be aware of is feeling thirsty. If you have feelings of thirst, this is a sign that your body is dehydrated, and you should drink water. The majority of adults should be able to recognise when they are thirsty and act on this by drinking water. However, it is helpful to be aware of other symptoms of dehydration, as they may indicate whether your body is mildly, moderately or severely dehydrated.

Some signs and symptoms of mild and moderate dehydration include:

  • Feeling thirsty.
  • Less frequent urination.
  • Urine that is dark in colour.
  • Feelings of dizziness or light-headedness.
  • Unusual tiredness, fatigue or lethargy.
  • Dry or sticky mouth.
  • Dry or cool skin.
  • Headaches.
  • Muscle cramps.

Some signs and symptoms of severe dehydration include:

  • Rapid heartbeat.
  • Rapid breathing.
  • A weak pulse.
  • Fits or seizures.
  • Confusion, lack of energy and irritability.
  • Feeling dizzy.
  • Extremely dry skin.
  • Pale skin.
  • Hypotension.
  • A reduced conscious state.
  • Fainting.

Signs and symptoms of dehydration in infants or young children

Infants and young children are at greater risk of dehydration than adults. One of the reasons for this is their low body weight and the increased frequency of which they experience vomiting and diarrhoea.

Some children are at greater risk than others, for example:

  • If they are less than one year old.
  • If they have a lower than average birth weight.
  • If they are experiencing an illness that results in a loss of appetite, difficulties swallowing or an inability to tolerate liquids.
  • If they are showing signs of malnutrition.
  • If they live in a hot climate.

Infants and young children are usually unable to tell an adult if they are feeling thirsty. When babies begin to wean off breastmilk or formula milk and begin eating solid foods, it is important that they drink water to account for the fluids that they are not getting from milk.

As infants and young children are usually unable to tell an adult if they are feeling thirsty, it is important that the adults who care for them ensure they are drinking enough water and look out for any signs of dehydration.

Some signs and symptoms of dehydration in babies and young children include:

  • Urinating less than four times a day or only urinating in small amounts.
  • Urine that is dark in colour and strong-smelling.
  • Dry mouth, tongue and lips.
  • Dry eyes.
  • Cold and blotchy hands or feet.
  • Listlessness or irritability.
  • Showing unusual signs of tiredness, lethargy or fatigue.
  • Sunken eyes or cheeks.
  • Sunken fontanelle (the soft spot on an infant’s head).
  • Producing few or no tears when crying.
  • An abnormally fast heartbeat or pulse.
  • Abnormally rapid breathing.
Baby drinking water to help with dehydration

Signs and symptoms of dehydration in the elderly

The signs and symptoms of dehydration in the elderly are similar to the signs in younger adults. However, as some elderly people may be unable to recognise signs of thirst or identify the signs of dehydration, it is important for other adults, particularly if the older person has a carer, to be aware of the signs of dehydration in the elderly.

Some of the signs and symptoms of dehydration in the elderly include:

  • Tiredness or fatigue.
  • A dry mouth.
  • A decrease in urination or urine that is dark in colour.
  • Sunken eyes.
  • Feelings of dizziness.
  • Confusion or disorientation.
  • Cramping in the muscles or muscle weakness.
  • A rapid heart rate.
  • A weak pulse.
  • Difficulties with movement or walking that are unusual for the individual.
  • Fainting.
  • An inability to sweat.
  • Low blood pressure.
  • Shrivelled skin.

If you are unsure if an elderly person you care for is experiencing dehydration, you can pinch the skin on the back of their hand and observe how quickly the skin returns to normal. If the skin maintains a tented shape for even one second, this could be a sign they are dehydrated.

What causes dehydration?

Dehydration can be caused by several different factors. Not drinking enough water, losing too much water, or a combination of both can cause dehydration.

It could be that you have not drunk enough water because you were too busy or forgot to drink, you have no access to water, you were too ill to drink, or you lacked the facilities or strength to drink.

Losing too much water is a common cause of dehydration. You may lose too much water as a result of:

  • Diarrhoea or vomiting – Repeated diarrhoea or vomiting can cause your body to lose a high amount of water and electrolytes in a short period of time.
  • High fever – If you have a high fever, you are more likely to become dehydrated. As your body temperature increases, your skin will become hot, flushed and clammy and your water levels will decrease.
  • Excessive sweating – You lose both water and electrolytes when you sweat. If you don’t replace the fluids you lose through sweat you will become dehydrated. You may sweat more than usual if you are exercising, the weather is hot or humid or you are ill.
  • Increased urination – You may urinate more if you have undiagnosed or uncontrolled diabetes, or if you are on certain medications that cause you to urinate more, such as certain blood pressure medications or diuretics.
  • Drinking too much alcohol – Alcohol is a diuretic, which means it makes you urinate more. Many people who drink too much alcohol will experience a headache the following day. This is a sign that your body is dehydrated. If you do not replenish the fluids you lost when drinking alcohol, your dehydration is likely to become more serious.
  • Diabetes – People with diabetes may be more likely to become dehydrated because they have higher levels of glucose in their bloodstream. Their kidneys will attempt to get rid of the glucose by producing more urine. This can cause you to become dehydrated.

Who is at greater risk of dehydration?

Although dehydration can happen to anyone, there are certain groups of people who are at greater risk of becoming dehydrated.

  • Infants and young children – There are several reasons why babies and young children have a higher risk of dehydration. As they have a low body weight, this makes them more sensitive to smaller amounts of lost fluid. They also lose a higher proportion of their fluids if they have a high fever. Furthermore, they are more likely to experience diarrhoea and vomiting. Infants and young children often cannot get themselves a drink or tell adults that they feel thirsty.
  • Older people – Elderly people are at greater risk of dehydration because their body’s fluid reserve decreases and their ability to conserve water becomes reduced as they age. They may also be less aware that they are becoming dehydrated as their sense of thirst becomes less acute. Elderly people are also more likely to have chronic illnesses and be on medication that raises the risk of dehydration. If an older adult lives alone, mobility problems may mean that difficulties getting themselves a drink or using the toilet independently can result in them drinking fewer fluids.
  • People with a long-term health condition – Health conditions such as diabetes and kidney disease can increase the risk of dehydration if the individual has increased urination. Certain medications that are used to treat some health conditions can also raise the risk of dehydration.
  • People with short-term illnesses – Anyone experiencing vomiting, diarrhoea or a high temperature are at a higher risk of dehydration because of the additional fluids they are losing from their bodies. Even having a cold, cough, sore throat or Covid-19 can result in dehydration as you may be less likely to eat and drink enough.
  • People experiencing alcoholism – Alcohol is a diuretic, meaning that it causes your body to remove fluids through urination at a much faster rate than other liquids. If a person who drinks alcohol does not drink additional water to replace what has been lost, they can quickly become dehydrated. If an individual with alcoholism is drinking alcohol every day, they may be less likely to replace the lost fluids or continue to dehydrate themselves daily.
  • Athletes – As the body loses a lot of fluid through sweat, athletes who sweat more are at greater risk of dehydration. It is important for athletes to drink additional fluids to replace the water and electrolytes they lose through sweat.
  • People at high altitudes – Increased urination, dryer air and more rapid breathing that people experience at higher altitudes can all result in dehydration.
Elderly woman fainted due to not drinking

Complications of dehydration

Dehydration can lead to serious complications, especially if it is not treated.

  • Heat exhaustion – This is when your body overheats and can lead to heatstroke, which is a life-threatening condition. Dehydration increases the risk of heat exhaustion as it reduces your body’s ability to sweat and maintain its normal temperature.
  • Urinary and kidney problems – Prolonged dehydration can cause a variety of issues, including urinary tract infections and kidney stones. You could also experience kidney failure which is a life-threatening condition whereby your kidneys are no longer able to remove fluids and waste from your blood.
  • Seizures – Seizures can occur due to electrolyte loss. Electrolytes help carry electrical signals between cells. If your electrolytes are imbalanced, the electrical signals may become mixed up. This can lead to involuntary muscle contractions and even a loss of consciousness.
  • Low blood volume shock – Also known as hypovolemic shock, this is one of the most serious potential complications of dehydration. It occurs when you suddenly lose a lot of fluids or blood from your body. Your blood volume then drops, meaning there is less blood circulating your body. This causes a drop in the amount of oxygen that is in your body and a drop in your blood pressure. This is a life-threatening emergency.
  • A coma – Dehydration can cause a decreased blood supply to the brain, which can lead to a coma and even severe damage to your organs.
  • Death – In cases of severe dehydration, reduced oxygen and blood flow can affect the vital organs. Cell and organ function may begin to fail, and death can occur.

How to prevent dehydration

Preventing dehydration is essential for protecting your health. There are several things you can do to help prevent dehydration.

Drink plenty of fluids

Adults need to drink between 2 and 2.5 litres of water every day. Replacing the fluids that we lose throughout the day is essential. According to Bupa, on average, adults lose 1.5 litres of fluids per day through urination, 500ml through sweat, and 200ml through defecation. Fluids are also lost through breathing. Be aware that the amount of water you need to drink can vary based on your age and your environment.

Drink more water if you are exercising

When you exercise, you usually produce a lot more sweat. In fact, one hour of exercise can produce up to 1.4 litres of sweat. The more you sweat, the more fluids you lose from your body. To prevent dehydration, it is important to replace any fluids you lose when exercising. Drink water before you begin exercising, during your exercise and once you have finished exercising.

Drink more water in a hotter climate

Similarly to when you exercise, you usually sweat more when the weather is hot or humid. Being inside with air conditioning also results in dryer air which can cause dehydration. Drink more water when the temperatures are higher, even if you do not spend a lot of time outside.

Drink water as soon as you feel thirsty

Thirst is a sign that your body is already dehydrated. Never ignore the signs of thirst and drink water as soon as you begin to feel thirsty.

Drink more water if you are ill

Vomiting, diarrhoea, bladder infections, influenza and bronchitis are some illnesses that can cause you to become dehydrated. Drink extra fluids if you are ill to account for any fluids you are losing from your body. Don’t wait for the signs of dehydration before you drink additional water if you are already unwell.

Tips for carers

If you are a carer of someone who is elderly or has other health conditions, it is extremely important that you ensure they drink enough fluids as they may be at greater risk of dehydration. Ensure they drink during mealtimes and ensure they always have water close by that they can drink themselves if they are physically able. It can also be beneficial to provide them with foods that have a high water count, such as fruits, vegetables, soups, ice cream and jelly.

People seeing a doctor due to medical issues

When to see a doctor

If you think that you or someone else is experiencing dehydration and the symptoms are not improving with treatment, you should see a doctor as soon as possible.

If the dehydration is severe, you will need to seek urgent medical help. You should call 999 or visit the Accident and Emergency (A&E) department of your local hospital if:

  • You are confused or disorientated.
  • You feel dizzy and the feeling does not go away.
  • Your pulse or heartbeat is weak.
  • Your pulse or heartbeat is rapid.
  • You are feeling unusually tired.
  • You have not urinated all day.
  • You experience fits or seizures.

The signs and symptoms of severe dehydration in babies and young children can be different. If your baby or child develops any of the following symptoms, you should take them to the doctor immediately:

  • If they are showing signs of drowsiness.
  • If their breathing is faster than usual.
  • When they cry, there are no or few tears.
  • If they have a sunken fontanelle.
  • If they have not urinated in the last 12 hours, or if their urine is dark in colour.
  • If their mouth is unusually dry.
  • If their hands or feet are cold or blotchy.
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About the author

Nicole Murphy

Nicole Murphy

Nicole graduated with a First-Class Honours degree in Psychology in 2013. She works as a writer and editor and tries to combine all her passions - writing, education, and psychology. Outside of work, Nicole loves to travel, go to the beach, and drink a lot of coffee! She is currently training to climb Machu Picchu in Peru.

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