60% of human body is water
Around 60% of the human body is made up of liquid. The liquid that we have in the body is called body fluid.
The body of a normal 70kg adult holds about 42 litres of body fluid.
So you may even say that human beings are made of fluid.
Even on a quiet day, people lose about 2.5 litres of body fluid each day, while on an active day people can lose much more. It is important to replace the lost fluids to keep a balance between fluid intake and fluid loss.
Humans cannot survive without body fluid. If the body loses just 3% (about 900ml in case of 60kg adult) of its fluid, dehydration symptoms such as fatigue will occur. With a 4-5% fluid loss, humans experience headache and dizziness. It can be fatal if more than 10% of body fluid is lost.
So go ahead replenish your body with adequate water.