To answer that question, you need to consider quite a few different criteria. First, consider how long you intend to stay out hiking. Depending on the weather and climate, you may need to drink quite a bit of water. For example, if the area that you are hiking in is relatively hot or humid, you’ll want to drink at least one liter per hour.
Considering that most adults barely drink two liters of water per day, you can understand how the capacity of your water bottle becomes very critical. So, if your intended hike is about four hours, and the conditions make you feel hot and sticky, you should try to drink about four liters of water in total.