Water is essential for life.
Many global guidelines recommend that women drink about two liters of water each day, and men 2,5.
But scientists say our need for water depends on several factors.
Not drinking enough water can lead to dehydration, but drinking too much water can also be deadly.
Water makes up about 60 percent of our body weight.
It is in our cells, organs, blood and in various pathways in our body.
"Water is a nutrient," says Dr. Nidia Rodriguez-Sanchez, a hydration expert at the University of Stirling, Scotland.
"We focus on protein, vitamins, carbohydrates, and fiber, but we don't think about water as an important nutrient in our lives."
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Water plays a key role in almost every bodily function.
According to Harvard Medical School, some of its key roles include:
- Transporting nutrients and oxygen to cells
- Flushing bacteria from the bladder
- Aid in digestion
- Preventing constipation
- Normalizing blood pressure
- Joint cushioning
- Protection of organs and tissues
- Body temperature regulation
- Maintaining electrolyte balance (sodium)
What happens if you don't drink enough water?
Human bodies are constantly losing water through sweating, urination, and even breathing.
In order to continue to function properly, this lost fluid must be replaced.
This process is called water balance.
When the body loses more water than it takes in, dehydration can occur.
This can lead to a wide range of health problems.
Symptoms of dehydration
- Dark yellow urine with a strong odor
- Urinating less often than usual
- Feeling dizzy or lightheaded
- Feeling tired
- Dry mouth, lips and tongue
- Sore eyes
In severe cases, dehydration can cause confusion, rapid heartbeat and even organ failure, according to the World Health Organization (WHO).
If you drink too much water, can it be dangerous?
Yes, and the consequences can be serious.
When excessive amounts of water are drunk in a short period of time, it can cause hyponatremia, also known as water intoxication.
This happens when the sodium balance in your blood becomes dangerously low, leading to swelling of cells.
U symptoms of hyponatremia include:
- Nausea and vomiting
- Headache
- Confusion
- Loss of energy, drowsiness and fatigue
- Restlessness and irritability
- Muscle weakness, spasms or cramps
- Epileptic seizures
- In extreme cases, coma
Joanna Perry trained with her daughter and son-in-law to participate in the London Marathon in 2018.
It was a very hot day and she drank large amounts of water that volunteers distributed to the runners.
"The last thing I remember was the sign for the half marathon," Joanna said on the BBC's show Food chain.
She woke up after three days in the intensive care unit.
A video taken by her husband shows her crossing the finish line.
She doesn't remember that.
"My partner and some other friends were there. They waved at me - I was physically unstable."
"We got home and I got really sick and passed out," she recalled.
"I literally drank so much water that I flushed out all the salts and nutrients you need to function."
Joan's case shows what happens when more fluid is introduced into the body than it can handle.
The liquid is quickly absorbed into the bloodstream.
Excess absorbed fluid is filtered by the kidneys, which then produce urine.
However, our kidneys can only process about a liter of fluid per hour.
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How much water do we really need?
To stay healthy, many health authorities recommend six to eight glasses of water a day.
The European Food Safety Authority recommends two liters for women and two and a half liters for men.
This includes water from all sources, including food, not just drinks.
Most foods, such as fruits, vegetables, rice, and even nuts, contain water.
Watermelon, for example, is about 92 percent water.
But even these recommendations may not apply to everyone.
Professor John Speakman, from the University of Aberdeen in Scotland, was part of a worldwide study that tracked the water intake of more than 5.000 people in 23 countries.
"Men between the ages of twenty and sixty probably need about 1,8 liters of water."
"And women in the same age group need 1,5 to 1,6 liters."
"By the time you're about 85, you actually only need about a litre a day," explains Professor Speakman.
But the amount of water an individual needs depends on factors such as body weight, amount of physical activity, age, gender and environmental conditions.
"The thing that has the biggest impact on how much water you need is actually how big you are," he adds.
"If you live somewhere warm and humid, your water needs will be significantly greater than someone who lives in a cold and dry place."
Thirst is the body's natural signal that it needs more water.
The color of your urine is another good indicator of hydration - pale yellow is a sign that you are well hydrated, while dark yellow could indicate dehydration.
You will also need to drink more fluids if you are sick and vomiting or have diarrhea.
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