Remember to choose the correct SIZE humidifier for the room. If the unit is too large, condensation may build up leading to bacteria and mold. Measure the square footage of the room and obtain a model for that size room. Humidifiers should have an AUTOMATIC SHUT-OFF feature so that it will turn off automatically if the reservoir runs dry. Use filtered or distilled water instead of tap water that contains minerals that breed microorganisms. Keep the unit very clean (every two to three days)....soak all parts in a 10% bleach solution and empty/dry the tank each time you are done using it.
Children's Hospital of Philadelphia