Crypto’s in the news this week — 14 people got sick from a hotel pool in Washington, and the pool was clean, well-maintained, no violations on record. That’s the thing about Cryptosporidium: chlorine doesn’t stop it. These are the same parasites behind every “boil water” notice you’ve ever seen. Giardia and Cryptosporidium — “Crypto” — are microscopic parasites that cause intestinal illness, and Crypto has one nasty trick: its protective shell shrugs off the chlorine your utility uses to disinfect the water.
What they are
Single-celled parasites spread through human and animal waste. When conditions turn bad, they form hard-shelled cysts (Giardia) and oocysts (Crypto) that survive in cold water for months. It takes as few as one to ten organisms to cause infection. Symptoms: diarrhea, nausea, vomiting, fever — miserable for a healthy adult, dangerous for the immunocompromised.
Where they come from
Surface water — lakes, rivers, reservoirs — contaminated by wildlife, livestock, or sewage overflows. Wells under the influence of surface water can carry them too. After heavy rain or flooding, the risk spikes. This is why utilities drawing from surface water must filter and disinfect to strict federal standards.
The health picture, honestly
For healthy people, giardiasis and cryptosporidiosis are usually self-limiting — a week or two of misery. For infants, the elderly, and anyone immunocompromised, Crypto can be life-threatening. There’s no MCL for either — the EPA regulates them through treatment requirements instead: utilities must achieve 99.9% removal or inactivation of Giardia and 99% of Crypto.
How to test
Specialized lab testing exists but isn’t routine for homeowners. Practically: if your utility issues a boil-water advisory, assume the worst. Well owners after floods or with surface-water influence should test for total coliform as a screening indicator and talk to their health department.
What removes them
Three proven answers: boiling (a rolling boil for 1 minute kills both — the CDC’s gold standard), absolute 1-micron filtration, and UV disinfection (very effective against both, including chlorine-resistant Crypto). Reverse osmosis removes them easily. Note the word absolute: a filter labeled “absolute 1 micron” is tested to block everything above that size. A filter labeled “nominal 1 micron” or just “1 micron” is not — the CDC specifically warns that nominal filters may NOT remove Crypto. NSF Standard 53 or 58 certification for cyst reduction is what you look for on the box.
What does NOT remove them
Chlorine and chloramine at normal municipal levels — Crypto is virtually unaffected. Standard carbon pitchers, water softeners, and sediment filters with loose micron ratings. “Effective against Giardia” on a label doesn’t mean effective against Crypto.
If a boil-water advisory hits your town
Don’t use your drinking water system during the advisory. Put whole-home filters in bypass mode — bacteria can linger in the filter media and in POE tanks. It might not cause trouble right away, but they’re susceptible to harboring it. After the advisory lifts, flush through the spigot — not the shower head — before putting anything back in service. If a shower head filter was used during the advisory, replace it just like the other filters. And if your RO was used, assume the prefilters and membrane are fouled — replace them and disinfect the tank as a precaution.
What I’d buy: a point-of-use filter certified to NSF 53 or 58 for cyst reduction with an ABSOLUTE (not nominal) 1-micron rating — or an under-sink reverse osmosis unit, which handles cysts plus everything dissolved. For whole-house protection on a private well, a properly sized UV system validated for Crypto inactivation.
This is the article where the micron rating lesson matters most: absolute versus nominal is the difference between protected and exposed. Read the label. If it doesn’t say “absolute,” it doesn’t count.
Curious what’s in your tap? Start with What’s In Your Water?
Leave a Reply