some of the signals your body gives you of a low water level are constipation, terribly dry skin, and increased incidence of urinary tract infections and reoccurring headaches.
there are ways other ingesting water that are beneficial to your body. A popular way to reduce fever is to take a bath in cool water. This helps bring down your entire body temperature, thus reducing fever. The use of water in this manner is called hydrotherapy. You will probably find you have used one or the other of these methods at some point.