For optimal health it's recommended you drink at least 8 glasses of water per day which keeps you hydrated and flushes out many toxins to help keep your kidneys healthy.
I you don't want to drink 8 glasses of water per day then as long as you're drinking at least a couple glasses of water per day then you'll be okay as well.
Of course the more water you drink the better because it helps to flush away those toxins but just don't drink too much water because it can lead to water poisoning which can kill you.