Dangers of dehydration: How much water should we drink each day?

Anyone can become dehydrated due to a plethora of reasons that range from physical activity to heat exposure and much more. It is easy to forget to stay hydrated throughout the day, but this is dangerous. We must keep replenishing fluids lost through sweating and eliminating waste.

While it may be easy to treat a mild case of dehydration at home, chronic dehydration can be more severe and life-threatening.

So, how do you know you are dehydrated?

How much water should you drink in a day?

Can you drink too much water?

And what are the dangers of dehydration?

We explore all these and more below with our own Alex Ruani, Chief Science Educator at The Health Sciences Academy and UCL Doctoral Researcher. 

How much water should we drink a day?

How much water we need per day depends on many factors – from age, gender and genetics, to body weight, height, physical activity levels, heat exposure, your diet, and several others. Being pregnant or lactating also means you’ll need some additional fluids than usual.

While there are no official ‘plain water’ intake recommendations, we can keep hydrated from a total fluid intake of a combination of drinks and food.

Below are the minimum fluid intake recommendations by the European Food Safety Authority (EFSA), with 20% to 30% of these amounts coming from food:

GroupRecommended total water intake (per day)
Infants (0-6 months old)100 – 190 ml per kg bodyweight, from breastmilk
Infants (6-12 months old)0.8 – 1.0 litres
Children (1-2 years old)1.1 – 1.2 litres
Children (2-3 years old)1.3 litres
Children (4-8 years old)1.6 litres
Boys (9-13 years old)2.1 litres
Girls (9-13 years old)1.9 litres
Men (older than 14 years)2.5 litres
Women (older than 14 years)2.0 litres

What are the benefits of staying hydrated?

Some of the key benefits of adequate hydration include:

  • enabling your brain to work properly,
  • maintaining your skin’s health and suppleness,
  • regulating your body temperature,
  • keeping a steady and rhythmic hormone production,
  • fomenting cell longevity,
  • aiding proper digestion,
  • cushioning your brain, eyes, and spinal cord, and
  • helping to eliminate harmful toxicants, metabolic by-products, and waste.

In essence, keeping us alive!

Can chronic dehydration impair weight loss?

Surprisingly, keeping hydrated throughout the day actually helps to mitigate weight gain. Even mild, chronic dehydration is correlated with increased body weight. How so?

Dehydration keeps the levels of a hormone called angiotensin II chronically high. As a result, this hormone which is supposed to maintain body fluid regulation stops working properly.

On the other hand, adequate hydration is associated with weight loss. For example, upping our fluid intake boosts lipolysis, a key process for fat loss.

And when it comes to hunger regulation, water pre-loading before a meal often leads to eating fewer calories in one sitting!

And if that wasn’t enough to convince you, drinking 500 ml of water increases metabolic rate by 30 percent!

What are the signs that you’re dehydrated?

Feeling thirsty!

When you feel thirsty, your body may already be dehydrated by 1% to 2%! Fluid losses of 1% to 2% generate the thirst sensation.

Did you know? By the time the brain signals thirst, the body may have already lost 1% to 2% of essential body fluids. This is because the brain can override feelings of thirst.

Fluid losses of 2% to 3% result in increased body temperature and impaired mental and physical performance.

A 4% loss leads to fatigue, nausea, vomiting, and diarrhoea.

Heat cramps, chills, nausea, clammy skin, and rapid pulse signal a fluid loss of 5%. The problem is that dehydration at this level can already be fatal, especially in children and older people.

Reduced sweat and urine production, weakness, headaches, dizziness, confusion, and dry mouth may indicate a severe 6% to 10% dehydration.

A fluid loss of over 10% can be life-threatening, leading to heatstroke, hallucinations, unsteady walk, and no urine or sweat produced.

What are the dangers of not drinking enough?

Death. Humans can die within days when going without any fluid intake. How long depends on the person and previous hydration status – with anything from a few days to about 10 days.

Dehydration occurs when the body uses or loses critical amounts of water that are not replenished.

When you’re chronically dehydrated, day in and day out, your urine colour will be darker, you may feel weaker, and you may experience frequent headaches.

Chronic, severe dehydration can result in serious unwanted complications, including gastrointestinal disturbances like constipation, urinary tract infections, kidney stones, skin ageing, increased cortisol levels and systemic inflammation, delirium, acute decreases in physical and mental performance, sudden drops in blood pressure (hypotension), swelling in the brain, and even seizures.

Not a pretty picture, so it’s important to make regular hydration a priority!

If you’re drinking enough during the day, then your urine should look pale and clear.

Do you need to drink more if you work out?

With exercise, you should be drinking the equivalent amount of what you’re sweating, plus a bit more if it’s hot and humid.

The harder and longer your exercise, and the hotter and more humid the environment, the more fluid you will lose.

During an hour of vigorous exercise, a trained individual could expect to lose around 1 litre of fluid – and even more in hot conditions.

During more strenuous exercise, in warm or humid conditions (e.g. marathon running), you could be losing as much as 2 litres an hour!

Unfortunately, the best way to know how much fluid you lose during exercise is to weigh yourself before and after without drinking anything.

Another less accurate way (but less taxing to your body) is to weigh yourself beforehand, drink a fixed amount of water during training, and weigh yourself again after your workout to measure any changes in body weight.

If your body weight is maintained, then the amount you drank would have probably been sufficient to compensate for fluid losses.

Electrolyte losses are usually replaced swiftly when eating unless you’re a competitive athlete or training in extreme heat conditions, where an electrolyte-rich drink may help.

Do you need to drink more in the heat?

Yes! When you are exposed to heat, your body can become dehydrated quicker through liquid sweat and evaporated sweat – the one we cannot see!  

For every litre of sweat that evaporates, we lose around 600 calories of heat energy from the body – and this process of ‘losing heat’ helps to cool the body and is an example of thermoregulation. In other words, water from your body is carried to your skin via your blood capillaries, where it evaporates so you can lose heat. 

So when you’re exposed to heat for a period of time, be sure to compensate for the extra fluid losses.

Chilled water should also help keep your body cool.

Can you drink too much water?

Drinking too much water at once can be fatal.

In particular, if sodium levels become too low or too diluted. This can literally drown your brain. 

Too much water at once can dilute the blood, while also causing levels of sodium, potassium, and other electrolytes to fall and a flood of water into brain cells. Severe hyponatremia or water poisoning can lead to sudden brain swelling, seizures, coma, breathing arrest, and death.

Hyponatremia can also occur if there is an underlying medical condition where the kidneys cannot process all the water (primarily by excreting it through urination). 

How can you acquire the expertise needed to effectively help your clients reduce the risk of dehydration especially when engaging in vigorous exercise?

Getting specialised by completing our Advanced Sports and Exercise Nutritional Advisor™ Certification is your first step towards acquiring the unique knowledge and skills for helping your clients make the necessary changes to their routines, diet, and lifestyle.  

During this certification, you will learn: 

  • Hydration strategies used by elite athletes and world-class champions
  • How to replace sweat losses
  • Effects of hydration on performance
  • Hydrating before, during, and after exercise
  • The science of sports drinks
  • Building a personalised diet plan for your client
  • Analysing your client’s food diary and fluid intake and much more!

Get the full details and PDF curriculum download here.  

You can also expand your professional opportunities with our Nutrition Accelerator Scholarship!

 Enjoy access to 1 of 14 certifications (including this Advanced Sports and Exercise Nutritional Advisor™ Certification).  

Grab the chance to become specialised so you can immediately begin to make an impact.  

Hurry over to our scholarship page to check your eligibility and learn more. 

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