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Two Liters Too Many? Unraveling the Confusion Around Drinking Water

Hydration is essential for human health, but the conflicting advice on this topic is a recipe for bewilderment.

Laura Simmons - Editor and Staff Writer

Laura Simmons

Laura Simmons - Editor and Staff Writer

Laura Simmons

Editor and Staff Writer

Laura is an editor and staff writer at IFLScience. She obtained her Master's in Experimental Neuroscience from Imperial College London.

Editor and Staff Writer

glass of water on kitchen counter
"Water, water everywhere" – but how much should you drink? Image credit: Pixel-Shot/

You don’t have to look far to find someone waxing lyrical about how drinking more water is the key to a previously untapped well of inner harmony. The human body is mostly made of water, after all.

The wellness influencer world abounds with conflicting views – if it’s not tricks to test your hydration levels or adverts for the latest drinking accessories, then it’s the worrying trend of the “no water” diet, devotees of which swear off drinking water altogether (not something we would recommend!).


Even official advice in this area can be a minefield; so, just how true is it that we should all be paying more attention to our hydration?

The official advice

In the UK, the NHS recommends that adults should consume six to eight cups or glasses of fluid per day, to include water, low-fat milks, tea, coffee, and other sugar-free beverages. That’s the first problem, right there – they don’t clearly specify exactly how large a cup or glass should be, so it’s hard to extrapolate from this the volume of liquid that is being recommended.

In the US, the advice is at least a little clearer. An adult woman’s daily intake, the National Academies of Sciences, Engineering, and Medicine suggest, should be 2.7 liters (11.5 cups); for an adult man, that increases to 3.7 liters (15.5. cups). However, this recommendation encompasses not only the fluid contained in drinks, but that contained in food as well – and it’s not that easy to figure out how much liquid you are eating in a day, never mind what you’re drinking.

Similar advice is produced by governments and health bodies all around the world. The consensus seems to be that somewhere between 2 and 3 liters is optimal for staying hydrated. So, where does this advice come from?

What happens when we don’t drink enough water?

It’s definitely true that not drinking enough water can have dangerous, maybe even fatal consequences.

Dehydration is caused by losing more fluid than you are consuming. The first sign that dehydration may be on the way is a pretty obvious one – feeling thirsty. As it progresses, you will notice that your pee is darker and more strong-smelling, you will feel tired and lightheaded, and you will have a dry mouth and tongue. 

People with certain health conditions, such as diabetes, are more at risk of dehydration. Your risk is also increased if, for example, you are sweating more due to exercise or hot weather, if you have diarrhea, or if you take diuretic medications to treat high blood pressure or other disorders. Babies and children are also at greater risk from complications associated with a lack of fluids.

Knowing the risks associated with dehydration may have you reaching for the latest TikTok-inspired cult water bottle to chug from all day long. Surely it’s better to be safe than sorry, right? 

water bottles
Thanks to influencer culture and reality TV (looking at you, Love Island), the humble water bottle has been transformed into a must-have accessory. Image credit: AndperfumeInd/

Unfortunately, it’s not quite as simple as that.

How much water is too much?

Since at least the early 1920s, scientists have understood the effects of excessive water consumption, known as water intoxication. The symptoms can be difficult to pin down, but can include nausea, vomiting, and an altered mental state which, if untreated, can progress to seizures, coma, and even death.

Sadly, there have been numerous high-profile cases of people becoming severely unwell from drinking too much water. Twenty-eight-year-old Jennifer Lea Strange died in 2007 after participating in a radio contest in which people were challenged to drink a large amount of water for a chance to win a Nintendo Wii – despite a caller ringing in to the program to warn the presenters of the dangers.

A woman in the UK became seriously ill after following advice to drink plenty of water to help her recover from a urinary tract infection. The huge quantity of fluid she consumed caused her to develop a condition call hyponatremia, where the body's sodium levels become dangerously low. Luckily, the woman received hospital treatment and recovered, but hyponatremia can be fatal.


Again, it's difficult to know the exact amount of water that would prove toxic for an individual – these particular cases involved drinking very large amounts in a short period of time, so you're unlikely to be putting yourself at risk during the course of a normal day. It's worth remembering, though, that you can have too much of a good thing.

Should we worry about our water intake?

So, we’ve established that the official recommendation of 2-3 liters of water per day is well-intentioned, given the risks associated with drinking too much and too little. But, should you panic if your bottle isn’t empty by the end of the workday? The answer is, no.

A number of experts weighed in on this issue, and they were united in their view that you don’t have to stick rigidly to the guidelines when it comes to staying hydrated.

As nephrologist Karen Dwyer said, the body has pretty robust ways of letting you know that it’s thirsty: "The best gauge of your hydration level is the colour of your urine. You should aim for light yellow in colour; if very dark then you're dehydrated and need more water; if clear (like water) then you don’t need so much water,” Dwyer told The Conversation.


"A one-size fits all approach is unlikely to be helpful," added gastroenterologist Vincent Ho. 

Jon Bartlett, a sports scientist, agreed. "A person’s daily water requirements are highly individual and dependent upon a number of internal and external factors."

If you have a medical condition that is likely to affect your hydration levels, it’s always best to seek personalized advice from your doctor. Otherwise, drink when you’re thirsty, and be mindful that you will need to drink a little more in hot weather or during exercise – but don’t beat yourself up if you don’t manage the magic eight glasses.


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