Giardia is a water borne protozoan parasite. It causes diarrhea, dehydration, cramping. The virulence is 10 cysts for disease to occur, and their suction discs damage the intestinal epithelial lining. It is common is child care centers, municipal facilities because chlorine does not kill it. Reservoirs are humans, raccoons, beavers, dogs, cattle. Treatment is albendazole or metronidazole.