Are YOU hydrated enough? What to drink – how much and when – for optimum health… and the warning signs your body is parched

Whether you’re a still, sparkling or tap water fan. the chances are that you’re not as hydrated as you think you are. 

Dehydration happens when your body loses more fluids – through sweat, urine and other basic bodily functions like breathing – than you take in.

As the human body is around 70 per cent water, dehydration can have serious repercussions, and if unaddressed for a prolonged period of time, prove fatal. 

Concerningly, a huge proportion of the UK population can be classified as dehydrated, with some online sources going as far as to say that more than half of Britons do not drink enough water on a daily basis. 

The NHS recommends that adults should aim to drink between two and two-and-a-half litres of water a day – and this includes the water present in squash, fruit juices, milk, tea, and coffee. 

Some fruits and vegetables can also count towards our daily water tally, nutritionist Jenna Hope tells the Daily Mail. 

‘Cucumber has the highest water content, but tomatoes and celery are also high,’ she says. 

‘From a fruit perspective, things like melon, watermelon and pineapple are also all very high in water, but they’re also high in sugar so be mindful of that.’ 

But even with so many (delicious) ways to keep our water levels at a decent level, millions of people fail to hit the target, placing themselves at a higher risk of becoming unwell, with complaints ranging from simply being constipated to falling into a coma. 

Another concern about being dehydrated relates to how the body reacts to stress. A study into the link between water intake and the ‘stress hormone’ cortisol, found that being under-watered increases your risk of developing heart disease, kidney problems, mood disorders and diabetes.

The research, which came out of Liverpool John Moores University and was published in the Journal of Applied Physiology last August, found a direct correlation between water intake and stress. 

The team found that individuals who drank less than 1.5 litres of fluid per day – around seven cups of tea – had a cortisol response to stress that was over 50 per cent higher than those who met daily water intake recommendations. 

Dr Daniel Kashi, a member of the study team, said: ‘Although the low fluid group did not report being thirstier than the high fluid group, they had darker and more concentrated urine, clear signs of poor hydration. 

‘An important observation was that poor hydration was associated with greater cortisol reactivity to the stress test. Exaggerated cortisol reactivity to stress has been associated with poor long-term health.’

We asked the experts to answer some of the most pressing questions about hydration – and why it matters.

How much water should I drink a day?  

The NHS’ suggestion that we drink between two to two-and-a-half litres of water a day needs to be used as a guideline not a hard rule, says John Young, Professor of Translational Clinical/Healthcare Research at Teesside University. 

‘When it comes to the amount of liquid we have to take on it, there’s no magic number, because it depends on how warm it is and it depends on how active we are,’ he tells the Daily Mail. 

‘The amount you need to take on on a cold winter’s day when you’re sat at your desk is totally different to when it’s the middle of summer and if you’re being active. 

‘Somebody running for a few hours or doing physical work outside – like a farmer – is going to need to take on litres and litres and litres of water in the summer, compared to somebody who might need less than a litre in winter.’

Dr Lindsey Hunt from Precision Hydration adds that people who exercise for more than an hour a day need to approach hydration differently. 

He tells the Daily Mail that they should consider adding an electrolyte product – a powder made up of minerals such as potassium, calcium, magnesium and sodium, which are lost through sweat – to their post-workout water. 

‘Most people get enough electrolytes during day to day life through the food they eat, and there’s no evidence that for anything under an hour, that electrolytes are beneficial. 

‘It’s only when we exercise and sweat for more than 90 minutes that electrolytes become really quite helpful.’ 

How does our body use water?  

Water is used to transport minerals, nutrients and oxygen around our body and into our cells, where it is used for every basic metabolic function. 

‘All our cellular processes depend on on water, and the way that our cells communicate with each other is often by chemicals that get passed through fluids,’ says Professor Young. 

‘If those fluids become more concentrated, it just stops our body from working.

‘Our blood is largely liquid, and we know that if we become even slightly dehydrated – by just one or two per cent – it will affect our blood pressure.’ 

Low blood pressure can cause people to fall, faint or feel a little bit light headed, and it can also affect our concentration levels.

Water also helps carry away metabolic waste products and excess minerals to the kidneys where it is expelled as urine.

Through sweat, water also helps maintain our body temperature, and it helps protect our organs by acting as a form of ‘shock absorber’. It also lubricates joints and tissues, eyes, nose and mouth. 

Water is also needed for osmoregulation, which is how the body strictly controls the concentration of salts both inside and outside cells, preventing them from bursting or shrinking.  

What happens when we get dehydrated? 

We tend to lose two to three litres of water each day through breath, sweat, urine and bowel movements — and if we’re not fully replacing that water loss, that is when we become dehydrated.

Even slight dehydration can have a big impact on the body and the brain. 

When it reaches a point of dehydration, the brain will send out hormone signals to divert water away from non-life-sustaining areas, such as the skin, muscles and joints. It does this in order to regulate function of more important organs such as the brain, heart and liver.

Dehydration can also trigger urinary tract infections (UTIs) as less water intake means less urine, and what is produced is highly concentrated. 

This allows bacteria in the bladder to thrive – and become harder to naturally flush out. 

Older people are particularly susceptible to dehydration – and developing potentially deadly UTIs.  

What are the signs of dehydration? 

The most obvious symptom of dehydration is feeling thirsty, but there are other – visible – warning signs. 

Dehydration usually becomes apparent when passing urine. You may realise that you’re going to the toilet less than usual, or that your urine has a dark yellow colour and a stronger smell than usual. 

You may also notice that your eyes look ‘sunken’ – in babies, the top of their head can also appear dipped inwards. 

Feeling tired, dizzy and lightheaded can also signal that your body is crying out for liquids. 

Other tell tale sign is if you have a dry mouth and tongue, and your lips start to go dry and flaky, and if your fingernails remain pale in colour for several seconds after being pressed on for three seconds. 

Ms Hope adds that sometimes feeling hungry can be a sign that your body is crying out for a drink. 

‘Often when you’re dehydrated, you can misinterpret those thirst signals for hunger,’ she says. 

‘People can often find themselves looking for a snack, thinking that they’re hungry, when actually they’re just thirsty.’

Can you be overhydrated? 

Drinking too much water- known as water intoxication or hyponatremia – can be fatal. It causes confusion, nausea, vomiting, headaches, and seizures. 

Frankie Phillips, of the British Dietetic Association, previously told the Daily Mail: ‘Drinking too much water too quickly – and we’re talking litres of water here, rather than cupfuls – can play havoc with the delicate balance of salts in the body.

‘If we drink a lot of water in a very short space of time, the kidneys can’t remove the excess fluid from our bodies quickly enough, and our blood becomes more diluted than it should be, with very low concentrations of salt.

‘The salt levels in blood and body cells are usually the same. But if the blood suddenly becomes more dilute, it can cause cells, in particular brain cells to swell. 

‘This can cause pressure in the skull, which can lead to headaches, and in serious cases, hyponatraemia or water intoxication, which can be fatal.’

Cases require hospitalisation, and patients will be treated by restricting fluid intake and, in severe cases, administering diuretics or intravenous sodium. 

What’s the best choice between tap, mineral and sparkling water?

For something that is technically tasteless, there’s a lot of varieties of water.

Breaking it down into the three most common choices of its raw form – that is, without additional flavourings – we have mineral, sparkling, and good old fashioned tap. 

‘From a hydration perspective, generally, all three are going to hydrate you in a similar way’ says Ms Hope. 

But there are some key differences. 

The most obvious is that sparkling – or fizzy – water is made gaseous by adding carbon dioxide during the production process, which can cause bloating, particularly in people who suffer with IBS. 

And when it comes to mineral water – your Evian, Fiji, Highland Spring et al – the differences are microscopic. 

Ms Hope explains: ‘They’re not necessarily going to be wildly different at all in terms of nutrition, the kind of the key minerals that you’ll find in mineral water are going to be things like magnesium, potassium, sodium, calcium, but there might be minor taste differences. 

‘This comes down to where the water’s sourced from and ever so slight changes in the mineral content of that area.’ 

There’s also a lot of ‘invisible extras’ in tap water – and not all of it is good for us. 

‘It very much varies depending on where you are in the country, but there is a concern around tap water having a slight contamination of things like heavy metals, forever chemicals, and microplastics,’ Ms Hope says.   

‘Generally, the consensus is it’s very safe to drink, but there’s no harm in having a filter jug, which can help to remove some of those contaminants from tap water.’