 to remove water from the stool. Otherwise we would rapidly dehydrate and die. That is why severe diarrhea is dangerous - the stool is moving through the colon and being expelled from the body so fast, there is no time to properly reabsorb the stool water back into the bloodstream.<br /><br />Conversely, if the fecal material remains in the colon too long, the water removal process may extract too much of the fecal water and leave the stool mass excessively dry and hard. It is just that simple.<