The microbial diversity of wastewater used for irrigation and fertilization was assessed using specific polymerase chain reaction (PCR) assays to detect and genotype several pathogenic protists including Cryptosporidium spp., Giardia duodenalis, Cyclospora spp., Eimeria spp. and Enterocytozoon bieneusi. A total of 220 wastewater samples (110 raw, 110 treated) and 12 sludge samples were collected from 2005 to 2008 from 18 treatment plants located throughout Tunisia. Except for Cyclospora, which was detected only once, E. bieneusi (61%), G. duodenalis (28%), Cryptosporidium spp. (27%) and Eimeria spp. (45%) were frequently observed in wastewater and sludge. Sequencing of PCR products showed that C. hominis, C. andersoni, G. duodenalis sub-assemblage A-II and E. bieneusi genotypes D and IV were the most prevalent. An analysis of the distribution of 209 internal transcribed spacer sequences of E. bieneusi originating from wastewater at the 18 treatment plants showed a similar genetic diversity, regardless of the geographical location. The identification of these parasite species and genotypes and of host-specific Eimeria species indicates that the microbial quality of wastewater was impacted by humans, livestock and rodents. Given the public health risks that some of these parasites represent, guidelines on wastewater usage are needed to minimize human exposure to these pathogens.