Many people have a habit: in the early morning, they often start brushing teeth, washing face, or cooking immediately after turning on the tap water, and some even drink tap water directly. But the latest research has found that overnight tap water often harbors a type of bacteria — Legionella. If a person is infected with this Legionella pneumophila, they may develop a symptom resembling pneumonia, a "strange illness" that doctors often treat as pneumonia initially, only to find the treatment ineffective. Patients generally experience central nervous system symptoms such as chest pain, drowsiness, irritability, depression, confusion, and disorientation. Some also have digestive symptoms like diarrhea, abdominal pain, nausea, and vomiting, with severe cases even causing death.