I've read about using willow trees for natural rooting hormone, but thought the water was not supposed to be boiled. If boiling does not destroy the hormone it would kill any microbes at least.
Here is a recipe I found:
Willow trees produce a natural rooting hormone.
Cut willow branches into 2-4" long pieces. Put the willow cuttings into a pot and cover with water. Place lid on pot and heat on low (do not boil) for two hours. Turn off heat, keeping pot covered and allowing to steep for at least 12 hours. The solution should now be dark brown. Strain and discard the branches.
Insert the base of fresh cuttings into the liquid and leave them there for 12-24 hours to absorb the hormone, then plant into your medium.
Store unused hormone in the refrigerator. It will keep for years.