How much? Half of your body weight in ounces. For example, I weigh 158 pounds. I need to drink 79 ounces. However, I would rather simply drink five (5) sport bottles of water. This way I won't flush out medicine. Another problem, if you are seriously obese, it may be impossible to drink that much water that half your body in ounces would be. So, make sure atleast (5) sport bottles.
A new reminder for me? Wearing five (5) rubber bands around my left wrist. Then, once I drink one (1) sports bottle of water, place one (1) rubber band on my right wrist. When there are no more ribber bands around my left wrist, I have finished water intake for the day.
Do you get bored of plain water? Use water enhancers, as they come in boxes of eight (8) to six (6) packets per box, mostly. You can find them at almost every grocery store. Also, use cucumbers, lemons, cinnamon sticks, etc. to flavor.
If your kitchen faucet water does not taste good, most bottled water is not expensive.
I am going over this topic as there are people who drink mostly soda and coffee every day. Maybe if you are one to avoid water, this article might inspire you to convert.