Water is essential to life. In fact, your body is mostly water. And about every 7 weeks, that water is renewed, mostly by what you drink. Each day, an average adult naturally loses 2.5 to 3 liters of water under normal conditions. That water must be replaced. A person can live 40 days without food, but will not survive more than 2 or 3 days without water. That’s why it’s so important to hydrate properly.