Product review (1 stars): POUR IT IN . . . BREATHE IT IN!
Bacteriostatic agents that are added to the water in humidifiers are not necessarily a good idea. These chemical disinfectants will be pumped into the air along with the water and are potentially irritating to the lungs. An outbreak of very serious lung disease occurred in Korea from certain types of humidifier disinfectants that are not commonly marketed in the United States.
The best way to keep microbes from building up is to discard what remains in the reservoir every morning and refill with fresh water. In addition, do a thorough cleaning every two or three days with soap and water. You can also use a mild disinfectant such as vinegar to wipe down the humidifier parts when doing this cleaning, but harsh disinfectants such as bleach are not necessary. Make sure you rinse well before putting the humidifier back together.
 (Dr. Gary Ginsberg, public health toxicologist, and lecturer at the Yale School of Public Health, 2015)