The general recommendation is to drink 2 litres or 8 glasses of water per day. To be more accurate and to calculate your individual requirments you can base your water needs upon your body weight as follows:

35ml per kg of bodweight.

So if you weigh 70kg then: 70 x 35 = 2450.

This means you need to take 2.45 litres of water daily (from food or drink)

If your not very good at drinking...