Diarrhea can cause loss of body fluids if it is severe. In severe diarrhea, the patient has watery stools, and the stools are lost like water. Moreover, the number of stools a day is very large, and the daily loss of body fluids is also very large, so it can cause dehydration. When dehydration is replenished, try to take it mainly by mouth, because oral rehydration has to pay attention to ionic disorders and to insufficient blood volume. If dehydration is severe, it can cause secondary damage to the kidneys. So diarrhea with dehydration should not be ignored and must be rehydrated regularly, and oral rehydration should be given as much as possible. If oral rehydration is not possible, intravenous rehydration is required. Oral rehydration solution is to put glucose, ionic sodium, ionic potassium and other trace elements inside warm boiled water.