Oocyst – An oocyst is the thick-walled spore phase of certain protists (sporozoans), such as Cryptosporidium and Toxoplasma. This state can survive for lengthy periods outside a host and is very resistant.

I know what a Cryptosporidium spore is but I must confess this was the first time I saw Oocyst.  So I looked it up on Wikipedia, the free encyclopedia.  The results are posted above.  I am in the process of writing a book and I came accross that word in “Final Long Term 1 Enhanced Surface Water Treatment Rule”.

A excerpt of the book is posted below.  I want to encorage everyone to use Wikipedia, It is a free site that I use often.  They are now taking donations to keep the site free.


Physical removal is critical to the control of Cryptosporidium because it is highly resistant to standard disinfection practices. Cryptosporidiosis, the infection caused by Cryptosporidium, may manifest itself as a severe infection that can last several weeks and may cause the death of individuals with compromised immune systems.  



Final Long Term 1 Enhanced Surface Water Treatment Rule


The LT1ESWTR extends further this necessary protection from Cryptosporidium to communities of fewer than 10,000 persons.  Today’s rule for the first time establishes Cryptosporidium control requirements for systems serving less than 10,000 persons by requiring a minimum 2-log removal for Cryptosporidium. The rule also strengthens filter performance requirements to ensure 2-log Cryptosporidium removal, establishes individual filter monitoring to minimize poor performance in individual units, includes Cryptosporidium in the definition of GWUDI, and explicitly considers unfiltered system watershed control provisions.


Twelve waterborne cryptosporidiosis outbreaks have occurred at drinking water systems since 1984 (Craun, 1998; USEPA, 2000a). The largest of the known outbreaks occurred in Milwaukee and was responsible for over 400,000 illnesses and at least 50 deaths (Hoxie, et al., 1997; MacKenzie et al., 1994); other known outbreaks have occurred in smaller communities and have involved many fewer people. An incident such as a rainstorm that flushes many oocysts into the source water or causes a sanitary sewer overflow combined with a water treatment plant upset could allow a large pulse of oocysts to move past the multiple barriers of a water treatment plant.


To read more about the “Final Long Term 1 Enhanced Surface Water Treatment Rule”


See the Fact Sheet at: http://www.epa.gov/safewater/mdbp/lt1eswtr_fact.html  or

For general information on the LT1ESWTR, contact the Safe Drinking Water Hotline, at (800) 426-4791, or visit the EPA Safewater website, http://www.epa.gov/safewater/mdbp/lt1eswtr.html.


For copies of the Federal Registernotice of the final regulation or technical fact sheets, contact the Safe Drinking Water Hotline at (800) 426-4791. The Safe Drinking Water Hotline is open Monday through Friday, excluding Federal holidays, from 9:00 a.m. to 5:30 p.m. Eastern Time.