There is no exact amount that you need to drink, but generally it is recommended that any person drinks at least 8 glasses of water per day.
You can replace some of the water with vegetables, fruit, soup, juice, milk or tea.
I think it's best to listen to your body, drinking just to satisfy thirst is usually enough. Many moms are so busy that they don't realize they are thirsty. Try to keep a bottle of water near you during the day while working.
You are getting in enough fluids if your urine is clear. So what I usually do is, check every time I urinate, if my urine is not clear I drink a large glass of water. Do this and your body should be hydrated enough for sufficient milk production.
