Water in the human body

Kim and Philip are stuck on a desert island. Come on Philip, we need to go find water. But I’m starving! I don’t have the energy to go looking for water. I need food first!

Philip, a person can survive three weeks without food, but only a couple of days without water. We need to find water first! Kim is right. Although we need both food and water, water is much more essential for survival than food. But why is water so important?

Water keeps us alive and helps our bodies function normally. Our body is made up of cells, and water is the basic component of all of them. Around two thirds of the water in our bodies is in the fluid that fills the cells, while the rest is in the fluid between cells. Water dissolves other substances very well, it’s a great solvent. Substances that our body needs to function, such as vitamins, minerals, proteins and carbohydrates are dissolved by water easily.

This makes these substances easy to use in different processes, for example cell repair and cell division. Water is also an important component of blood. So not only does water dissolve these valuable substances, it also transports them and oxygen around the body. But water also dissolves substances that are harmful or that the body doesn’t need anymore - toxins and waste. Toxins and waste then leave the body together with water, in the form of urine.

Another function of water in our body is helping to keep our body temperature stable. Water can absorb and store heat very well, but it can also help release the body’s heat if needed, for example by sweating. When there isn’t enough water in the body, heat impacts us much more, for example it might cause muscles to cramp. Not only does water stop muscles cramping, it also reduces friction in our joints. So water is extremely important for the proper functioning of our bodies, but how much of our body is actually water?

That depends on the age, sex and fitness level of the person. Infants have a much higher percentage of water in their bodies than adults, typically between 75-78%. The amount of water in adults is lower, on average between 57 and 60%. The amount of water is usually higher in men than in women, because women naturally have more fatty tissue which contains less water. For our body to work normally, this amount of water needs to remain constant.

We lose between 2 to 3 litres of water every day, mostly through urine and sweat. This is why it’s important when we lose water, to regain it by eating food and drinking water. But you’ll need to drink more than usual if it’s a hot day or you’re exercising, which makes you sweat more. Kim and Philip are feeling thirsty now, which means they have already lost 2-3% of their body’s water. If they lose even just a little more water, their physical coordination will get worse and they’ll find it difficult to think clearly.

Am I just imagining it or is there a stream over there? We’re saved!