Coccidial oocysts are the vegetative life stage of the parasite causing coccidiosis . Outside the body they are very hard to kill with disinfectants. This is why typically farmers mix coccidiostats in with the feed to kill the parasite inside the animal when it is more susceptible. We advise not to treat drinking water with Halamid or any other disinfectant, while dosing medication, including coccidiostats.