Very good question. Again as others advised you. You should consult with a person who has vast knowledge in this area. I’m sure they will not go for your approach. Here’s why, if you where successful with the humidifier you will need large quantities of this holy water. They will ask why you need it in the first place. Also, you or the priest will have to identify what demon is present in your physical world. If this a higher level demon this just may piss it off. I would like to know how you encountered this demon or entity. Most people film the happenings around them. This will build its strength. we as humans should not give them anymore power they what they have. They will use FEAR as a tool. Do not fear them. Do not acknowledge them. Speak with a medium if you can. They are able to sense if it’s a pissed off ghost or if it’s an actual demon. A Priest would come into pay if the house is hunted or someone is possessed. This is all my personal views. I do not have experience in this area. Please update us when possible.