Frequent Questions

On the ?Unfiltered System Inactivation Requirements? slide, can the 2-log protection be provided by one disinfection method or must it come from a combination of treatment?

Systems must use at least two disinfectants, one of which must be chlorine dioxide, ozone, or UV light.  Crypto inactivation can be accomplished by any one of these three disinfection methods.  In other words, using free chlorine to meet virus and Giardia inactivation requirements and using UV light to provide 2-log Crypto inactivation is sufficient.

For additional guidance on the Long Term 2 Enhanced Surface Water Treatment Rule please visit

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