How to tell if you're dehydrated – from feeling tired to splitting headaches

With temperatures continuing to rise this week, it’s important that we all drink enough water as dehydration can be dangerous – but do you know all the side effects?

A woman looking upset as she holds a glass of water
It’s important to stay hydrated during a heatwave (stock photo)

Brits are basking in the summer sun this week as the UK heatwave reaches its peak.

And while the weather is gorgeous, spending too long in the sun can have some nasty side effects – not least of all the bright red sunburn some of us will be dealing with in the days to come.

Hot weather also means we need to make sure we’re drinking plenty of water and really pushing for that two litres a day benchmark, as the rising temperature can make dehydration set in much faster than usual.

But how successful are we at staying hydrated, and would we know the symptoms of dehydration if they struck?

Not drinking enough water doesn’t just leave you feeling thirsty – it can have some nasty side effects that you need to watch out for while you’re soaking up the sun this week.

You may feel tired or have a headache (stock photo)


Getty Images)

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Feeling really tired

One of the signs of dehydration is actually fatigue, which may explain why you sometimes get an energy slump during the day as your body’s intake of water slows down.

According to Yahoo!, our blood pressure will drop if there’s not enough water in our body, which causes the blood flow to the brain to slow down and our heart rate to speed up.

When combined, these things can all lead to a feeling of tiredness.

Low blood pressure

Over half of our blood is made up of plasma, which itself is made up of water, protein, and salt.

This means that if you’re not drinking enough water, your blood will become too concentrated – which slows down the blood flow to the vital organs which need it.

Muscle cramping

As a result of your blood becoming more concentrated, you may find that your blood volume drops which in turn causes muscle cramping – which is never a pleasant feeling.

When your blood volume drops, your body has to prioritise and focuses on sending blood to the heart above all other parts, so your muscles receive an inadequate flow, causing cramps.


Headaches can be caused by all sorts of things, but did you know that dehydration is a very common migraine trigger?

This is because when your brain doesn’t get enough fluids to function properly, a range of symptoms such as headaches, migraines, fading in and out of consciousness and dizzy spells may follow.


The digestive system needs plenty of water to run smoothly, and if you’re not drinking enough, then your intestines will pay the price – as water helps food flow through the digestive tract without getting stuck.

So if you’re feeling constipated during this heatwave, try drinking more water to help get things moving.

Dry skin

It’s easy to forget this sometimes, but your skin is an organ and, as such, it needs a healthy blood supply in order to function well.

We all know that applying moisturiser can help with dry skin, but it’s just as important to hydrate from the inside too with plenty of water.

Changes to your wee

In the same way that your digestive system needs water to function, so does your renal system.

Water is key in assisting our kidneys to remove waste from the blood by turning it into urine, so with less water in your body, you reduce the need to wee – which is bad news because this means that waste is still in your body.

You may also find that when you do go to the toilet, your urine is much darker than it should be, as it gets darker the more concentrated it is. You should really aim for a pale or straw-coloured wee.

Dry mouth

Do you know that gross cottonmouth sensation you sometimes wake up with?

It’s a sign from your body to have a glass of water because it can’t make sufficient saliva if it doesn’t have enough fluids. Bad breath can also be caused by a dry mouth – so reach for the H2O as well as the mouthwash.

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