Women need to have nine cups of water, this number changes according to your LifeStyle. The more active you are the more you will need to replace fluids. When working out be aware of your environment because you will need to drink more water if the temperature is very hot (likely to make you sweat more) or very cold(which can stunt your ability to sense dehydration), according to The Institute of Medicine. If you are thirsty you are already DEHYDRATED!!!!!