Many irrigated perimeters with treated waste water were created in Tunisia. The treated waste water reuse is now in full development. The perimeter of Cebala, 3200 m2, the most important in Tunisia (52 per cent of all treated waste water irrigated areas), is the subject of our study, namely the evolution of parasitic load of treated waste water in irrigation 'Network System'. In the summer season of 1992, samples were collected at the outlet of sewage treatment stations and at the treated waste water distribution sluices, in order to study the parasitic quality (hilminth eggs and protozoa cysts) during their transportation.