Water is one of the vital ingredients for life on Earth, but what happens to us if we suddenly can’t get this precious liquid?
The river wasn’t far away. Chaz Powell could see the Zambezi churning over boulders in the gorge a few hundred meters. It was tantalizingly close, but out of anyone’s reach.
In most developed countries, accessing clean water is as simple as turning on a tap. People in these places pour gallons of it down the drain every day without a thought, as they brush their teeth, shower, and flush the toilet. But around 1.1 billion people lack access to safe drinking water around the world, and a total of 2.7 billion find water difficult to access for at least one month of the year.
Water is one of the fundamental ingredients for life on Earth and our bodies are mainly composed of it. When we are forced to go without water, things can turn nasty very fast indeed.
Even mild dehydration can leave us feeling more tired and less able to perform physically
When exercising in a hot environment, the human body can lose between 1.5-3 litres (2.6-5.3 pints) of water every hour due to sweat. Another 200-1,500ml (0.3-2.6 pints) can be lost as moisture in exhaled breath, depending on the humidity of the surrounding air.
The effect this can start to have on the human body is profound. Even mild dehydration can leave us feeling more tired and less able to perform physically. As we lose more water, our ability to cool down through sweating also decreases, making overheating more of a risk.
With more water leaving our bodies than coming in, our blood starts to thicken and become more concentrated, meaning our cardiovascular system has to work harder to keep our blood pressure up.
Our kidneys try to compensate by retaining more water through reduced urination, water also rushes out of our cells into our bloodstream, causing them to shrink in size. When we lose 4% of our body weight as water, blood pressure drops and fainting can occur.
The third stage, when 7% of body weight is lost, is organ damage. “Your body is having trouble maintaining blood pressure,” says Lobo. “To survive, it slows blood flow to non-vital organs, such as your kidneys and gut, causing damage. Without your kidneys filtering your blood, cellular waste quickly builds up. You’re literally dying for a glass of water.”
Water scarcity is predicted to become more common due to climate change (Credit: Alamy)
Yet some people can not only survive such severe dehydration, but they can also even still keep performing at high levels.
As dehydration worsens it can affect how our brains work, disrupting our mood and our ability to think clearly
“Although it may be safe to drink urine in the short term to rehydrate, the physiological response to dehydration is to conserve salt and water,” says Lobo. “Urine output decreases, and ultimately the human can develop acute kidney injury and anuria (where the kidneys fail to produce urine). Hence, the quantity of urine in the medium-term will not be enough to sustain adequate hydration.”
Dehydration can also cause vital parts of the cardiovascular system, such as the blood vessels, to harden, increasing the risk of a heart attack
Being dehydrated in a hot climate only compounds the problem.
“The body is unable to regulate this heat which causes key enzymes in normal metabolic pathways to be destroyed, causing organs like the brain, heart, and lungs to de-function,” says Cookson. Eventually, this can lead to seizures, coma, and, as organs start to fail, death.
Exactly how long someone can survive without water is still largely debated. Most scientists agree humans can only go for a few days without taking in any food or water