Cryptosporidium & Giardia (Cysts)

Category: microbiological

Written by WaterFilterMatch Editorial TeamApril 2026

EPA MCL

Not regulated

Status

EPA Regulated

NSF Standard

NSF/ANSI 53 (cyst reduction), NSF/ANSI 58

Health Effects

Gastrointestinal illness including severe diarrhea, stomach cramps, nausea, and dehydration. Cryptosporidium can be life-threatening for immunocompromised individuals. Both parasites form cysts that are resistant to chlorine disinfection.

Source: EPA National Primary Drinking Water Regulations

Where It Comes From

Protozoan parasites found in human and animal fecal waste. Cysts are highly resistant to chlorine - a key reason why filtration is critical for surface water systems.

Where It's Commonly Found

Surface water supplies, agricultural areas with livestock runoff. Chlorine-resistant - outbreaks have occurred even in treated municipal systems (e.g., Milwaukee 1993 Cryptosporidium outbreak affecting 400,000+ people).

Regulated via treatment technique under the Surface Water Treatment Rules. All surface water systems must achieve 99.9% (3-log) removal of Giardia and 99% (2-log) removal of Cryptosporidium. Filters rated at 1 micron absolute or smaller effectively remove cysts.