Here is some information on PP from the EPA indicating it may not be effective against ghiardia or cryptosporida.
Section 5.4.4.3
"No information pertaining to protozoa inactivation by potassium permanganate is available in the literature. However, based on the other disinfectants discussed in this report, protozoa are significantly more resistant than viruses; therefore, it is likely that the dosages and contact times required for protozoa inactivation would be impractical."
http://www.epa.gov/ogwdw000/mdbp/pdf/alter/chapt_5.pdf
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