That happens to be a life saving fluid replacement and partial electrolyte expedient replacement.
Many people die in times of emergency because of fluid losses.
This can be from burns, vomiting, or diarrhea. The body needs water and certain water soluable chemicals to function. If either or both of these drop below a certain level, you die. There are many non-fatal diseases like cholera that become fatal due to lack of simple things like proper fluid replacement. If you have ever had a bad case of diarrhea and start to have pain in your muscles or joints, congratulations, you have had the early warning symptoms of a potassium deficiency.