Humidifiers are designed to help you breathe better, but depending on the type you have and the water you use, it might also be affecting your air quality at home. "It's not that I am saying humidifiers (are) completely bad for people. It's just we should be aware that the water quality we put into the humidifier is directly reflecting the quality of the indoor air you're breathing," said Ran Zhao, an assistant professor of Environment Chemistry at University of Alberta.