Why Do We Need Water?

If you were stranded on a desert island, you might be able to survive for a few weeks without food. But that’s only if you have fresh water. Take that water away and you’ve only got a few days to be rescued.

That’s because your body needs water as an essential nutrient — as the essential nutrient, really. Water makes up about 50% to 65% of your body weight, and it does much more than just quench your thirst. Every organ, tissue, and cell in your body needs water to function and keep you alive. 

But what exactly makes H₂O so special? Why is it so essential for your body to run? There isn’t one reason, but several.

Blood, Sweat, and Tears

First and foremost, water is the delivery system for your body. It makes up about 90% of plasma, which is the liquid base of blood, carrying crucial nutrients throughout the body, as well as the hormones that regulate everything from growth to metabolism.

Without enough water, your blood can thicken, slowing down circulation, which can lead to high blood pressure. Water also is critical for healthy kidneys, as they use it to filter nearly 40 gallons of blood each day, flushing waste out of the body through urine.

Through tears, water keeps the eye clear of debris and irritants. Through sweat, it plays a huge role in regulating your core body temperature. As sweat evaporates, it cools the skin and helps keep the body temperature stable. Without enough water, you stop sweating, which can lead to dangerous heatstroke. You also need to replenish the water you lose through sweat to avoid dehydration.

Even the joints — where two bones connect — rely on water. Cartilage, which is tissue that cushions and reduces friction around joints, is made of mostly water. Water keeps your cartilage healthy and spongy and lets your joints move easily. Without enough water, you could end up with painful joints during physical activity, such as exercising or even walking.

Water is the main component of cerebrospinal fluid, too, which is the protective shock-absorber that protects your brain and spinal cord from sudden jerks and shocks. You may not think of water the same way you do iron or steel, but it serves as a protective shield, like an inside-out suit of armor.

Water isn’t just the body’s armor, but also its power plant. Every second of every day, billions of chemical reactions happen inside your body to create energy, build proteins, and repair tissues. Water makes these happen. 

Take digestion: It uses a chemical process called hydrolysis, in which water breaks down proteins into amino acids and starches into simple sugars, enabling your cells to absorb and use them for energy. 

Water does this by splitting into separate parts – a molecule of H₂O splits into two, with one H (hydrogen) breaking off from the other H and the O (oxygen). These simpler components latch onto molecules found in proteins and starches to pull them apart into more digestible pieces.

Because your body uses it for so many things, you need a lot of water — healthy adults typically require between 11.5 and 15.5 cups each day. That also means you can quickly become dehydrated. So drink your water. Flavor it if you have to. Cucumber, lemon, and mint are popular options. 

You’re not just quenching your thirst — you’re giving your body what it needs to protect you, power you, and keep you cool.