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FilterScored

Contaminant · Water

Cysts (Cryptosporidium and Giardia)

EPA treatment-technique requirement (no numeric MCL) for Cryptosporidium and Giardia. 4 of the water filters we score hold an accredited NSF, WQA, or IAPMO certification to reduce Cysts (Cryptosporidium and Giardia). A claim is not a certification.

What it is

Cysts are the dormant, shelled form of two waterborne parasites, Cryptosporidium and Giardia (the bugs behind many "stomach flu" outbreaks traced to water). They get into drinking water through fecal contamination from humans or animals, often when surface water carrying runoff, sewage, or agricultural waste reaches a supply. The reason they matter is that tough outer shell: it lets the organism survive in water for a long time and shrug off the standard chlorine that handles most germs.

Why it matters

The EPA regulates Cryptosporidium and Giardia under its Surface Water Treatment Rules using a treatment-technique requirement rather than a numeric maximum contaminant level - in plain terms, utilities must filter and disinfect to set standards instead of hitting a single concentration number. Because these cysts resist chlorine, they are the reason a boil-water advisory goes out when treatment is disrupted. What we score is whether a filter is certified to reduce this contaminant, not any health outcome.

What removes it

Cyst reduction is a mechanical claim under NSF/ANSI 53, usually met with a roughly 1-micron absolute filter that physically strains the cysts out, or with reverse osmosis certified to NSF/ANSI 58. Here is the catch: an ordinary carbon pitcher is not built to a tight, guaranteed (absolute) pore size and is not certified for cysts, so do not assume it removes them. Certification specifically for cyst reduction is what separates a filter verified to handle these parasites from one that only claims general filtration.

Reference: EPA Surface Water Treatment Rules (treatment-technique requirement, Cryptosporidium and Giardia); NSF/ANSI 53 (cyst reduction) and NSF/ANSI 58 (reverse osmosis).

Scored filters certified for Cysts (Cryptosporidium and Giardia)

FAQ

Does a Brita or other carbon pitcher remove Cryptosporidium and Giardia?
Not unless that specific pitcher is certified to NSF/ANSI 53 for cyst reduction. Most basic carbon pitchers are built to improve taste and reduce chlorine, not to the roughly 1-micron absolute pore size needed to strain out cysts, and we found no accredited cyst certification for typical carbon pitchers - so do not lean on a standard one for this. Look for an NSF/ANSI 53 cyst claim on the product, not a general filtration claim.
Does boiling water remove cysts?
Here boiling actually helps. It is not filtration, but bringing water to a rolling boil is exactly the step public-health agencies point to during boil-water advisories, because heat inactivates Cryptosporidium and Giardia. A filter just gets there a different way, by physically removing the cysts - which is why we score filters on whether they carry an NSF/ANSI 53 cyst certification or reverse osmosis certified to NSF/ANSI 58.

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