Cryptosporidium
Crypto·Affects skin,
A chlorine-resistant parasite that causes severe diarrheal illness. The 1993 Milwaukee outbreak sickened 400,000 people and killed at least 50.
Crypto
EPA limit
99% removal required (Treatment Technique)
Most at risk
Immunocompromised, AIDS patients, organ transplant recipients, infants, elderly
Found in
Well water
AquaOx filters
YesViqua UV sterilizer (downstream pairing)
What it does to you
Health effects
Cryptosporidiosis presents two to ten days after exposure as profuse watery diarrhea, stomach cramps, nausea, and low-grade fever. Healthy adults clear the infection in one to two weeks, though symptoms can wax and wane for up to 30 days.
For immunocompromised people the picture is far worse. In AIDS patients, transplant recipients, and others with weakened immune systems, cryptosporidiosis can become chronic, profuse, and fatal. There is no reliable cure: the standard antiparasitic nitazoxanide is only effective in patients with functioning immune systems.
The Milwaukee 1993 outbreak remains the largest waterborne disease event in US history. A treatment plant failure allowed Crypto oocysts from Lake Michigan into the city supply, and roughly 403,000 residents fell ill. At least 50 people, mostly AIDS patients, died as a direct result.
Where it comes from
How it gets into your water
Cryptosporidium exists in drinking water as oocysts, a hardy egg-like form with a tough outer shell. Oocysts are shed in the feces of infected humans and animals, particularly cattle, and enter surface water through agricultural runoff, sewage discharge, and wildlife contamination.
The reason Crypto is dangerous in chlorinated supplies is that the oocyst shell makes the parasite essentially immune to chlorine at normal disinfection doses. The only municipal defenses are physical filtration and UV inactivation, which is why the EPA's Long Term 2 Enhanced Surface Water Treatment Rule requires extra Crypto controls at plants drawing from at-risk surface sources.
Private wells fed by springs or shallow groundwater near pastureland are especially vulnerable. Oocysts can survive months in cool, moist soil and travel through fractured rock and karst geology.
Agricultural runoff
Cattle and livestock feces shed oocysts
Surface water intakes
Lakes, rivers, springs serving wells or utilities
Treatment plant failures
Crypto resists chlorine; needs physical removal or UV
Recreational water
Pools and water parks are common transmission routes
Find out for yourself
Is it in your water?
Municipal utilities serving surface water are required by the EPA to monitor source water for Crypto and adjust treatment if oocyst counts climb. Most do not report Crypto numbers in the annual Consumer Confidence Report because detection in finished water is supposed to be zero, but boil-water advisories are issued whenever monitoring or filtration performance triggers concern.
Private wells in agricultural regions or karst terrain (limestone with fractures and sinkholes) are the highest-risk category. There is no quick home test for Crypto: lab analysis requires a specialized immunofluorescence assay. If you are on well water and live downhill from grazing land, periodic professional testing is the only way to know.
If anyone in your household has unexplained prolonged diarrheal illness, especially someone immunocompromised, ask your doctor specifically to test for Cryptosporidium. Standard stool panels often miss it.
The fix
How AquaOx filters it
The AquaOx whole-house system attacks Crypto from two directions. First, the upstream 1-micron absolute pre-sediment filter physically traps Crypto oocysts, which measure 4 to 6 microns. NSF/ANSI Standard 53 recognizes 1-micron absolute filtration as a valid mechanical barrier for Cryptosporidium cysts. The carbon and KDF stages downstream do not inactivate the parasite chemically.
For a complete microbial barrier, AquaOx pairs the whole-house system with a Viqua UV sterilizer installed after the filtration stages. UV at 254 nm scrambles the DNA inside the oocyst, rendering it unable to replicate even if it physically passes through. Crypto is somewhat UV-resistant compared to bacteria but well within the dose range of a properly sized residential UV chamber.
For homes on surface-fed wells or in agricultural areas with high Crypto risk, we recommend the filter-plus-UV pairing as the baseline configuration. Filtration without UV leaves a gap. UV without pre-filtration loses effectiveness because turbidity shields the oocysts from the UV dose.