The Transcend 365 miniCPAP requires the use of distilled water for proper function of the heated humidifier. Failure to use distilled water will damage the heating element within the humidifier and may require repair or replacement. Alternatively, this compact & portable water filter kit filters tap water and is approved for use with your Transcend 365 miniCPAP. It’s a great alternative to distilled water when you’re traveling or when distilled water is not readily available to you.