How much water does a female 45 years old need to drink on a day?

Generally, however much you weigh in pounds, you should drink the equivalent in ounces. So, if you're 125 pounds (not saying you are, of course), you should drink about 62 or so ounces. More if it's hot or you are exercising.

The key is drinking good quality water though - not juice, soda's, coffee or anything else. Your body is roughly 70% water and you need to replace what you lose through elimination and physical exertion with water. If you do a lot of physical exercise, you may need to add salt to your water intake.