Everyone is different. It depends on your lifestyle, how active you are, how hot it is, even how much you are talking, etc. A general rule of thumb is about 1/2 ounce per pound of body weight per day.
For every cup of coffee, tea or glass of alcohol, increase your water intake by one and a half cups to counterbalance the diuretic effect of these beverages.
Buy yourself a nice stainless steel water bottle to bring with you wherever you go. Keep a big glass of water at your desk.
Increasing your water intake is a simple and effective way to improve your health,
Cheers!