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Wisconsin Department of Safety and Professional Services





Plumbing Products Register

Contaminant: Cysts

This designation includes oocysts of cryptosporidium parvum, toxoplasma gondii, and, cysts of giardia lamblia and entamoeba histolytica.

Point-of-use (POU) water treatment devices approved for cyst/oocyst reduction will only reduce the concentration of cysts/oocysts at water outlets that are served by the devices.  POU water treatment devices are typically designed to treat water for a single outlet or a small number of outlets, such as the cold water at the kitchen sink and the cold water line serving an icemaker.  Therefore, using point-of-use devices such as these will not protect all routes of potential exposure.  Potentially hazardous exposures to cysts/oocysts will remain possible at unprotected outlets.

The presence of cysts and/or oocysts strongly suggests that other disease causing organisms may also be present (e.g. bacteria, virus).

If, by way of reputable water analyses, a water supply is known to contain cysts/oocysts, then all the water entering the residence must be treated at the point-of-entry using an approved water treatment device to address all potential routes of exposure.

For further information on cysts/oocysts and microbiological safety, consult:

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