Your body loses fluids when participating in strenuous exercise, high temperature sweat, or down with fever or illness that causes vomiting or diarrhea. If you lose fluid for one of these reasons, it is important to increase fluid intake so that you can restore the natural moisture levels in your body. Your doctor may also recommend you to drink more fluids to help treat other health conditions, such as infections of the bladder and urinary tract stones. If you are pregnant or breastfeeding, you may want to consult your doctor about your fluid intake because your body will use more fluids than usual, especially if you are breastfeeding.