According to doctor people should drink around 8 glass that is 2 liter water per day. But the amount of water depends upon the body structure of the people.
First know your weight, you need to know weight in order to know how much water you need to drink. Because the amount of water for the weight of 47 and 80 differs. Water helps to take out the impurities from the body as well as it is important for metabolism and digestion of the body.
Divide your weight with 30 and you need to drink water as the result. If your weight is 60 than you need to drink 2 liter water. People who weighs 80 kg must drink 2.6 liter water.
When you do exercise your body takes out more sweat and due to lack of water and dryness you need to drink one glass water 30 minutes after you do exercise. You need to drink juice and fruits more.