It's a pretty simple question with no easy answers. The truth is, that it depends on many factors how much water you need, including your health, how active you are, what you do for living, where you live, …
Every day you lose water (breathing, sweating, urine, …) and for your body to function properly, you must replenish its water supply by drinking enough water and eating foods that are rich with water (you can see which ones are here).
So how much water does the average, healthy person need? Researches showed that an adequate intake for men is about 3 liters (or 6 EQUA bottles) of total beverages a day, and for women is about 2.2 liters (4,5 EQUA bottles) of total beverages a day.
Although no single formula fits everyone and knowing more about your body's need for fluids will help you estimate how much water to drink each day.
Some people also ask: Is it is possible to drink too much water?
We're always told to "drink, drink, drink", but sometimes it can also be too much. In fact, overhydrating can be just as dangerous as being extremely dehydrated, but it’s much harder to reach the state of over hydration, than dehydration. Drinking small amounts of fluids at regular intervals is the key, to staying properly hydrated. You shouldn't ever feel "full" of water though.