- Chlorine and Cryptosporidium

"The venue for the symposium was the city [Milwaukee] where , in 1993 400,000 people were infected by Cryptosporidium oocysts that were present in the tap water. Many of those infected suffered symptoms such as cholrea-like diarrhea, abdominal pain, nausea, vomiting and weight loss. More than 50 people died as a resulf of the outbreak. Water chlorination does not inativate the oocysts, which is why they have to be removed by the treatment process. .. The number of Crystosporidium oocyts in water should be fewer than 1 in 10 liters in order for the water to be considered safe to drink."

Lars Gillberg. in Small Systems can Protect Against Waterborne Pathogens, in Water Technology, March 2000 - (http://www.waternet.org)