ET-4B1A (2/8/05 version)
Pathogens in Surface Waters: Why is This a Drinking Water Problem?

The protozoan parasite Cryptosporidium is a potential contaminant that is particularly threatening to surface water sources of drinking water. This was demonstrated in 1993 when the City of Milwaukee public water supply became contaminated with Cryptosporidium, leading to several deaths and hospitalizing thousands more. The Milwaukee water treatment plant filters were unable to remove the tiny microorganisms and chlorine could not destroy them. There are many potential sources of Cryptosporidium in watersheds, including septic system discharges and nonpoint sources associated with animal feces.

Therefore, the Enhanced Surface Water Treatment Rules (ESWTR) will require public water systems to provide additional treatment to protect against Cryptosporidium and allow for the development of a watershed control program that reduces the water supply risk of contamination from Cryptosporidium and other pathogens.