Why drinking a lot of water isn’t as good for you as you might think

Water is said to stimulate your metabolism, help you lose weight, improve your complexion and promote your health in countless ways. In recent years, clear water has become a symbol of purity, beauty and slimness. Anyone who’s active on Instagram will probably be familiar with large water bottles as a ubiquitous lifestyle accessory of popular influencers.

In fact, adults need one to one and a half litres of water every day. But too much fluid can be harmful to your health. This is particularly true for athletes, but also for people who don’t eat much and fight their hunger with water.

Why too much water is risky

American actress Brooke Shields experienced this first-hand. She suffered a severe epileptic seizure several months ago after drinking too much water. The actress – best known for the series Susan – shared her experiences of water poisoning in an interview in Glamour magazine.

What happened? The fluid balance in the body is regulated by a close interaction between electrolytes, especially sodium – which we absorb in the form of table salt – and water. Drinking too much water lowers the sodium concentration in the body. If our water intake exceeds the kidneys’ excretion capacity, the body can no longer get rid of enough water. This causes the cells in the brain to swell – the technical term for this is cerebral oedema – resulting in headaches, dizziness, nausea, coordination problems, tremors, unconsciousness, seizures and even a coma.

The difficulty is that the symptoms are similar to those of dehydration, i.e. a lack of fluid. If you’ve never heard of water intoxication – or hypotonic hyponatremia in medical jargon – you may make the mistake of drinking more water. This confusion makes matters worse. Untreated water poisoning can be fatal.

How much do we have to drink?

To get to the bottom of the phenomenon of water poisoning, I interviewed an expert. Dr Michael Joannidis (article in German) is head of the intensive care unit at the Innsbruck University Clinic for Internal Medicine and has studied the topic in detail. His publications include a specialist training course for doctors in the journal Medizinische Klinik – Intensive and Emergency Medicine (website in German).

«We have a very well-regulated system that controls our water intake via the thirst signal,» explains the doctor. This works very well for adults up to the age of 70 to 80, he adds. Drinking more – in anticipatory obedience so to speak – isn’t necessary. Drinking more can only help with specific illnesses such as gout or kidney stones. According to the expert’s findings, the assumption that drinking more improves the function of diseased kidneys hasn’t been proven.

That’s why he’s sceptical of the trend of drinking a lot of water. «It’s a bit of a lifestyle thing and also an industry-triggered error,» he says. He also considers the habit of no longer leaving the house without water – even for short appointments – to be questionable for health reasons. «If I can’t go an hour without water, maybe I have a tic that forces me to drink constantly.» It’s very unlikely that people in this part of the world will develop a relevant water deficiency, even if they don’t drink anything for half a day.

However, for healthy adults who eat a normal diet, a little too much water isn’t a problem. This is because the extra fluid would simply be excreted through their urine.

General recommendations for water quantities quickly become problematic, because a man weighing 105 kilos needs more fluids than a woman weighing 55 kilos. The climate, physical activity and hormonal processes also have an impact. Anyone who eats a lot of fruit and vegetables also absorbs fluid through their food, which they then no longer need to drink. As we could spend days calculating our actual water needs, our bodies offer us useful support. «Drinking when you’re thirsty is still the most sensible thing to do,» says medical professor Michael Joannidis.

Who excess water can be dangerous for

Things are different for athletes who also lose salt through sweating. This can lead to a rapid drop in sodium levels and water poisoning. Studies state that around eight per cent of participants have reduced sodium levels after marathon runs. This figure can be up to 20 per cent for ultrarunners. Ironman triathletes, swimmers, mountain bikers and cross-country skiers are also affected.

People who want to lose weight, eating only unsalted fruit and vegetables or nothing at all and drinking large amounts of water to suppress their feeling of hunger, can also suffer from water poisoning. The 75 Hard challenge, which is popular on TikTok, encourages strenuous workouts and drinking four litres of water a day. According to media reports, Canadian TikToker Michelle Fairburn ended up in hospital with water poisoning as a result of the challenge.

It’s not just the amount, but also the length of time in which fluids are consumed that can increase the risk. An American woman died after downing four bottles of water in 20 minutes on a hot summer’s day, according to media reports.

Full disclosure: I’ve also fallen into the trap of drinking too much. Before a competition in Spain, I took the advice to stock up on fluids too much to heart. I drank water until my urine turned the recommended pale colour. A short time later, I fainted. Luckily, when I came to, I didn’t accept the water offered to me and ate some salty crisps instead. The race started without me, but I recovered as the day went on.

How to avoid water poisoning

If you eat enough, don’t follow a special diet, are sceptical of TikTok fitness challenges and lifestyle trends and focus on your feeling of thirst, your risk of water poisoning is low.

Athletes know how to help themselves with electrolyte drinks. The sodium they contain maintains the balance in the body so that the kidneys can excrete excess water. During long-distance races, food stations often offer salty snacks such as crisps, which also provide sodium. Sports food manufacturers also offer special salt tablets for extreme endurance competitions in scorching temperatures.

You can also make electrolyte drinks yourself by adding a pinch of salt, a little sugar and lemon juice. But not everything that’s commonly considered an electrolyte drink actually is one. Let’s talk beer: generations of athletes drank «recovery beer» after sweaty workouts to restore their electrolyte balance. Unfortunately, that’s not enough: «Beer isn’t an isotonic solution,» says medical professor Joannidis. He thinks this is more like wishful thinking on the part of athletes.

In fact, there’s such a thing as beer drinker syndrome, where people who drink litres of beer over several days without eating anything end up in hospital because of water intoxication. This is rare, but it shows that drinking when you’re thirsty can actually have dire consequences.