Water is a key factor in the life cycle of many parasite species. The devel
opment of the free-living generation (oocysts, cysts, eggs, larvae) and the
longevity of the resulting infectious stages are extremely dependent on th
e availability of water. Damp stables are principally associated with an in
creased risk of parasite infection. Infectious stages may accumulate in dir
ty watering equipment and in pools of water on pasture. Utilization of surf
ace water, especially when contaminated with sewage or effluent from sewage
plants, imposes an increased risk of parasite infection on farm animals. F
looding of pastures with water containing parasite stages can lead to exten
sive contamination. Rainfall, flooding or inadequate land disposal of manur
e may contaminate surface water with parasite stages of animal origin from
adjacent agricultural areas.