We speed up metabolism.

4. Drink more! When your body is dehydrated, your organs, especially your liver, work less efficiently, causing your metabolism to slow down rapidly. Research shows that if you lose at least 3% of your weight through fluid output (for example, if you weigh 63 kg, fluid = 2 kg), you slow down your metabolism by 2%. Dehydration can also cause fatigue and decreased muscle function. If you are actively exercising, then the water consumption may increase.