Giardia lamblia is a protozoan parasite known to be an important waterborne pathogen. The faeco-oral
transmission of the parasite leads to the presence of its cysts in the environment. Giardia cysts are
abundant in surface water worldwide. Knowledge of the prevalence of Giardia cysts in water resources
is important for controlling its transmission. The present study was designed for detection of G.
lamblia cysts, its seasonal variability, count and viability assessment in water supplies of Assuit
University Hospitals and Faculty of Medicine; using flow cytometry. Forty eight water grab samples
(20 liter per sample) were collected from water supplies of the faculty and hospital's buildings from
inlet, outlet and tanks during winter and summer 2014. All water samples were subjected to
filtration, elution and concentration followed by flow cytometry. G. lamblia cysts were detected in
14 water samples with detection rate of 29.2%. The highest rate of positive samples was recorded in
winter. The mean cysts number was 1066.3 cysts/L in summer and 837.1 cysts/L in winter. The percent
of viable G. lamblia cysts reached 6.2% in summer and 5.75% in winter with insignificant difference.
The results of the present study reflected the need for more efficient methods adapted by the water
treatment facilities in this locality for controlling the quality of drinking water. The results
demonstrated the benefit of flow cytometry as a rapid and simple method for evaluation of Giardia
cysts in water samples