Water is undeniably essential for life, but what exactly happens to your body when you are deprived of this crucial element?
The human body begins to shut down rapidly without water, leading to organ failure.
Imagine being stranded without water, the very substance that sustains us. This was the stark reality faced by expedition guide Chaz Powell as he trekked along the Zambezi River. He could see the river, tantalizingly close, yet completely inaccessible from his precarious position atop a gorge. “I can’t describe how thirsty I was,” Powell recounted, highlighting the primal panic that surged as his body screamed for hydration. He was beginning to feel the ominous signs of overheating, his body temperature soaring to alarming levels. Powell’s experience offers a visceral glimpse into the critical role water plays and how swiftly its absence can become life-threatening.
For many in developed nations, access to clean water is an effortless turn of a tap away. We often take for granted the sheer abundance, using gallons daily for mundane tasks like brushing our teeth or showering. However, this is a stark contrast to the reality faced by 1.1 billion people globally who lack access to safe drinking water, and a further 2.7 billion who experience water scarcity for at least one month each year. Water is not just a commodity; it is a fundamental necessity, comprising a significant portion of our bodies. When water is withheld, the consequences can be rapid and severe.
Chaz Powell’s Zambezi expedition turned perilous when he was cut off from water.
Powell’s ordeal unfolded during a solo expedition to traverse the length of the Zambezi River. Two months into his journey, having traced the river from its Zambian source, through Angola, Namibia, and Botswana, he encountered treacherous gorges on the Zambia-Zimbabwe border, near Victoria Falls. The terrain transformed dramatically. “The gorges are steep sloped cliffs,” Powell explained, describing the formidable landscape that stretched for approximately 150 miles. Compounding the challenge was the season: August 2016, the region’s hottest period, with temperatures reaching a scorching 50°C (122°F). He had chosen this time to avoid the Barotse Floodplains, which are submerged for most of the year.
Initially, Powell’s trek progressed smoothly, covering around 20 miles (36km) daily. However, the gorges drastically slowed his pace. “I had walked maybe a couple of miles a day, if that, just going over boulders,” he said, emphasizing the arduous terrain. This snail’s pace meant traversing the gorges could take a month, and with dwindling food supplies and no human contact, his situation grew precarious. The only signs of life were baboons and the powerful rapids within the gorge.
After two weeks navigating the treacherous gorge, Powell realized the need for an alternative route. His map indicated a substantial river feeding into the Zambezi. “I thought to myself I can get on the top it’s going to be about 20km (12 miles) to get to this other river,” he considered, estimating a potentially quick four-hour walk. He was unaware of the harsh landscape that awaited him above the gorge.
Worldwide water access remains a critical challenge affecting billions.
The initial indicator of dehydration is thirst, a signal that arises when the body loses just 2% of its weight in water. Human bodies are composed of approximately 60-70% water–70% of water, varying slightly with age. We constantly lose water through natural processes like urination, perspiration, respiration, and bowel movements. This lost fluid must be replenished through drinking and food intake. Around a third of our water intake comes from the food we consume. Insufficient water intake leads to dehydration.
“When thirst kicks in, your body clings to all remaining moisture,” explains Dileep Lobo, a professor of gastrointestinal surgery specializing in fluid and electrolyte balance. The body initiates a conservation mode. Kidneys reduce water sent to the bladder, resulting in darker urine. Sweating decreases, causing body temperature to rise. Blood thickens, and the heart works harder to maintain oxygen levels, increasing heart rate.
Dehydration rates are influenced by environmental factors and physical exertion. In a 50°C (122°F) climate, coupled with strenuous activity, the absence of water can rapidly become fatal. “Humans have an upper limit to heat tolerance, beyond which we suffer heat stress and even death,” Lobo cautions. While cold temperatures also pose risks, extreme heat dramatically increases mortality rates.
Even mild dehydration impairs physical and cognitive functions. During exercise in hot conditions, the body can lose 1.5-3 liters (2.6-5.3 pints) of water per hour through sweat. Exhaled breath can account for an additional 200-1,500ml (0.3-2.6 pints) of water loss, depending on humidity.
The consequences of dehydration manifest quickly. Even mild dehydration causes fatigue and reduces physical performance. As water loss increases, the body’s ability to cool itself through sweating diminishes, heightening the risk of overheating. Blood thickens and becomes more concentrated, forcing the cardiovascular system to strain to maintain blood pressure. Kidneys attempt to conserve water by reducing urination, and water shifts from cells into the bloodstream, causing cellular shrinkage. A 4% loss of body weight as water can lead to a drop in blood pressure and fainting.
At 7% water loss, the body enters a critical stage of organ damage. “Your body is having trouble maintaining blood pressure,” Lobo states. To prioritize survival, blood flow is diverted from non-essential organs like kidneys and the gut, leading to damage. Kidney failure results in a buildup of cellular waste in the blood. This stage is a severe medical emergency.
Climate change is projected to exacerbate water scarcity globally.
Remarkably, some individuals can endure significant dehydration and maintain high performance levels. Long-distance runner Alberto Salazar, during the 1984 Olympic Marathon in scorching Los Angeles heat, reportedly sweated approximately 3.06 liters (5.4 pints) per hour and lost 8% of his body weight. However, Salazar had immediate access to rehydration and a medical support team.
Back in the Zambezi gorge, Powell, without water and facing dire circumstances, activated his SOS phone. The US-based emergency service struggled to find local help, amplifying his panic. Desperate, Powell dug into the soil to seek coolness and resorted to drinking his urine, combined with a rehydration sachet.
Urine in a healthy individual is about 95% water, with the remainder composed of waste products like salts and ammonia. In dehydration, urine becomes even more concentrated, resembling seawater. “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,” Lobo clarifies. Urine production decreases, and kidney injury and anuria (kidney failure to produce urine) can develop. Urine, therefore, is not a sustainable rehydration source. Rehydration salts without sufficient water can further disrupt electrolyte balance, potentially leading to seizures and brain hemorrhage in extreme cases of electrolyte imbalance.
Confined to his hole, Powell cooled down slightly but continued to dehydrate. He recalled a documentary about heatstroke and began to fear he was experiencing the same. The SOS team eventually arranged a helicopter rescue, but with a four-hour wait. Powell, fearing he wouldn’t survive that long, decided to attempt a perilous climb down the cliff. “I’d rather die falling down a cliff than sitting here,” he remembers thinking. He fell 15ft (4.5m), injuring his nose.
His decision to climb, possibly impulsive, might have been influenced by dehydration itself. As dehydration worsens, brain function is impaired, affecting mood and clear thinking. Blood flow to the brain and brain volume decrease. Even mild dehydration (2% body water loss) can impair short-term memory, vigilance, arithmetic skills, and coordination, especially during strenuous activity in hot environments. Some studies link dehydration to delirium, particularly in the elderly.
Dehydration significantly reduces physical stamina and performance.
Driven by adrenaline, Powell continued his descent, clinging to the cliff face. Reaching a ledge, he fainted briefly. “My hands were bleeding, my face was covered in blood, my legs were bruised,” he described. Yet, he persevered for almost an hour until he reached the river. He spent an hour rehydrating and cooling down before contacting rescuers to confirm his safety.
“Chaz saved himself by finding a supply of water and shade,” notes Natalie Cookson, an emergency medical trainee doctor. Shade reduced his body temperature, slowing dehydration. Crucially, access to water allowed rehydration. “Dehydration is reversible and by replacing body water, a full recovery is likely,” Cookson confirms.
Without rehydration, Powell’s kidneys would have likely failed. Insufficient water flow allows toxins to accumulate, causing kidney malfunction and potentially acute tubular necrosis, a condition that can require weeks to recover from even with rehydration. Heart strain would have caused irregular heartbeats, low blood pressure, and potential seizures. Dehydration also hardens blood vessels, increasing heart attack risk.
Heat exacerbates dehydration. “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,” Cookson explains. This can lead to seizures, coma, and ultimately, organ failure and death.
The exact duration of survival without water is debated. Most experts agree that humans can only survive a few days without water and food. A 1944 study where two scientists deprived themselves of water for three and four days while consuming dry food, showed swallowing difficulties and facial pallor by the experiment’s end, but it was stopped before dangerous conditions developed.
Powell’s timely return to the river allowed crucial rehydration and cooling.
Individual water needs and tolerances vary. Evidence suggests the body can adapt to regular water intake levels. The longest documented survival without water is the case of Andreas Mihavecz, an 18-year-old Austrian bricklayer, who survived 18 days locked in a police cell in 1979 after being forgotten by officers. This extreme case is recorded in the Guinness Book of World Records.
While extreme dehydration is rare for most, four billion people face severe water scarcity at least one month annually. Climate change is predicted to worsen water access globally, with estimates suggesting two-thirds of the world’s population may face water shortages by 2025.
Powell’s ten-hour ordeal without water in extreme heat was a harsh lesson. After a week’s rest in Livingston, he continued his journey, completing it in 137 days. His experience underscored the vital importance of water. “I certainly don’t take it for granted anymore,” he affirms.
