The viability and longevity of Giardia cysts in the environment is significantly affected by temperature; as the temperature increases, survivability decreases. A small fraction of cysts can withstand a single freeze thaw cycle. Cysts may remain viable in water for long periods of time under typical environmental conditions. Survival in water is dependent primarily on decreased water temperature; no relationship was found between cyst survival and water pH, dissolved oxygen, turbidity, color, hardness, ammonia, nitrate or phosphorous. After being stored in water for 77 days at 8/ C, G. lamblia cysts were found to be viable by dye exclusion testing (Bingham et al., 1979). Cysts survived about 26 days at 21/ C and about 6 days at 37/ C. Less than 1% of cysts survived freezing at -13/ C for 14 days. Raising the temperature to boiling immediately inactivated the cysts. G. muris cysts were found to be infective in mice after periods of 28 days storage in distilled water at 5/ to 7/ C; none were found infective after 56 days (deRegnier et al., 1989). G. muris cysts remained viable for 2 to 3 months when stored in natural surface water at temperatures of less than 10/ C. The thermal death point (i.e., the lowest temperature at which G. muris cysts are inactivated in 10 minutes) is 54/ C (Schaefer et al.,
1984).