Our bodies are made up of 80 % water. Water plays a vital role in supplying oxygen to cells, as well as temperature regulation, waste removal and the everyday running of all major organs.
You can go about four weeks without food, but only three days without water.
If you wait until you're thirsty before you reach for that glass, then you're already dehydrated.
When the body is dehydrated, it often sends out signals that are misread as hunger pangs. Mild dehydration actually slows down body metabolism, so you're losing out on two counts if you let your water intake slip.
A little dehydration can leave you feeling tired as well as messing with your short-term memory. Start to feel a bit parched, and simple mental tasks could seem like a massive challenge.