water It depends on how much waste water that person gives out (e.g sweating, urination). the amount of water a human must drink in a day is 2 to 2.5 litres. the amount of water a human can drink in a day is 0 to 20 litres.(it depends) but an average human drinks 3-5 liters
If you drink six to eight, eight-ounce glasses of water a day, that is usually enough water for a human. However, if you're thirsty, drink more, and don't drink too much too late in the evening, because you may be awakened by the urge to eliminate the water you drank so late.
A human is supposed to drink 8 glasses of milk a day, but most of the time people don't. Water is healthier for you than milk but milk has protein so u can go either way. But ode say drink 4 glasses of milk and 4 glasses of water to even them out.
If you are talking about Drinking water then according to scientist a normal person should drink 12 glass of water a day which is equal to 3 liters, because a human being wastes a huge amount of water a day through Urine and Perspiration.