City of Alexandria

Cryptosporidium is a microbial pathogen occasionally found in surface water across the United States. While filtration removes Cryptosporidium, even the most advanced filtration methods cannot guarantee 100% elimination. Fairfax Water maintains strict filtration protocols according to regulatory standards to maximize removal efficiency.

Our monitoring occasionally detects these microorganisms in water sources. Current testing methods cannot determine if these organisms are viable or capable of causing illness. Consuming Cryptosporidium may lead to cryptosporidiosis, which causes symptoms like nausea, diarrhea, and abdominal pain. While most healthy individuals recover within weeks, those with compromised immune systems, infants, children, and elderly people face higher risks of serious complications.

We advise immunocompromised individuals to consult their healthcare providers about appropriate precautions. Cryptosporidium requires ingestion to cause illness and can spread through multiple vectors beyond water, including person-to-person contact, animals, swimming pools, food, soils, and any surface not properly sanitized after contamination.

Fairfax Water monitors both the Potomac River and Occoquan Reservoir in compliance with the EPA's Long-term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR Round 2). This regulation aims to increase protection against microbial pathogens in public water systems using surface water sources. Monitoring began in April 2015 and included monthly sampling for two years, concluding in March 2017. Under these guidelines, average Cryptosporidium concentrations determine whether additional treatment measures are necessary. Concentrations above 0.075 oocysts/Liter trigger enhanced water treatment protocols. Fairfax Water's raw water consistently tested below this threshold during the 2015-2017 monitoring period.

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