CPAP machines require a source of humidification to prevent dryness and irritation in the airway. Using regular tap water in the humidification chamber can result in the buildup of mineral deposits, which can be harmful to the machine and the user. The mineral buildup can cause damage to the machine and also release harmful particles into the airway. In addition, tap water can contain bacteria, viruses, and other contaminants, which can be harmful if inhaled or cause infections.