This article is from the Water Treatment FAQ, by Patton Turner with numerous contributions by others.
Hydrogen Peroxide can be used to purify water if nothing else is
available. Studies have shown of 99 percent inactivation of
poliovirus in 6 hr with 0.3 percent hydrogen peroxide and a 99%
inactivation of rhinovirus with a 1.5% solution in 24 minutes.
Hydrogen Peroxide is more effective against bacteria, though Fe+2 or
Cu+2 needs to be present as a catalyst to get a reasonable