For a time last week, all girls’ bathrooms at one South Philly elementary school were closed, with 400 students diverted to a single stall. Water leaked through the ceiling into the teachers’ lounge.

Qin Rao, MD, is a board-certified physician based in New York City. He currently works as a gastroenterologist and hepatologist at Manhattan Gastroenterology. Diarrhea and constipation are common ...