Could tapwater be contributing to outbreaks of stubborn perioral dermatitis?

Since toothpaste and mouthwash contain floride, as well as tap water, I decided to use purified bottled water at room temperature to rinse and wash my face. I started yesterday using purified bottled water and today I've noticed a slight difference in the size of the tiny bumps on my face, the bumps appear to be smaller and less noticeable! I was also wondering if you could boil tap water to remove all the chemicals and floride in it and then once the water has cooled to room temperature, use it to wash and rinse my face with it. QUESTION: Are those chemicals evaporated into the air or does chemical residue settle to the bottom of the pot, thus necessitating the avoidance of stirring the cooled boiled water, but gently dipping it out with a cup? :) Tweet