If you go to the Patron Saints Index (see the Related Link at the bottom of this answer) and click on the category "Beatified by" then you'll find a list of popes. Click on a pope's name and you'll...
water
If I'm not mistaken, that's water that was purified by "reverse osmosis"
The aspergillus is used by the priest to sprinkle Holy Water.
rain water is in the distilled form so we can say that it is pure