My mom just bought a honeywell coolmist ultrasonic 1 gallon no filter humidifier for her cat Sheba. Sheba gets itchy so we are hoping it will help her itches and the dry air in the apartment. Mom used it last night and woke up with white dust on things from using the tap water. Its mineral deposits I think. Is there anything she can add to the tap water in the humidifier that is still cat safe? She doesn't want to buy lots of distilled water because it adds up in price and it is heavy for her to carry with her rhumetoid arthritis. Does anybody know of anything we can add to the tap water in the humidifier and keeping it cat safe?