After you open a bottle, PA will start to grow in it. And tap water has a lot more in it than just water, from harmless things like sodium to less-nice things like chlorine.

So either sterile water or boiled distilled water is the way to go. And after you open the container of sterile water, unless it is the kind of dispenser that allows no contact with the environment, after that first use, you will need to boil the water to make sure there is no PA.

Boiling for 7 minutes is usually enough, unless you are at a high altitude, when you need to boil water.