Presence, Viability and Determinants of Cryptosporidium Oocysts and Giardia Cysts in the Addis Ababa Water Supply and Distribution System

The water supply and distribution system in Addis Ababa, Ethiopia, was investigated for the presence of viable Cryptosporidium and Giardia. A total of 115 samples were collected from water sources, treated water storage tanks, and tap water. Microbial sample collection and analysis were according to U.S. EPA method 1623. The physical and chemical water parameters were also determined in each water sample. Viable Cryptosporidium oocysts and Giardia cysts, collectively referred to as (oo)cysts, were found in two-thirds of the surface raw water samples. Only one of the three raw well water samples had viable oocysts and none had viable cysts. Of the treated water storage tanks, 35% had oocysts (none were viable), and 29% had cysts (only viable in one case). Of the tap water samples 21% had oocysts and 7% had viable oocysts. 1% of the tap samples had cysts, 6% had viable cysts. Turbidity was the only parameter found to correlate with the presence of (oo)cysts. While only one of the treated water storage tanks had viable (oo)cysts, the presence of non-viable (oo)cysts is indicative of problems with the water treatment system. The presence of viable (oo)cysts in the tap water samples showed contamination of treated water during distribution, potentially from underground sewage. There was a statistically significant decrease in free chlorine from the storage tanks to the tap. 22% of the tap samples had no measurable free chlorine. This situation poses health risks to residents of Addis Abba, especially to those with compromised immune system.