Abstract: The invention relates to a soil irrigation system comprising subterranean distribution pipes for distributing water to overlying soil, each pipe having a perforated upper wall whose outer surface is covered with water permeable means for preventing said overlying soil from fouling the perforations of said upper wall, and means integral with the remaining wall structure of said pipe for retaining said water permeable means in its covering relationship with said upper wall; said water permeable means being a unitary layer of capillary material which, in addition to its antifouling function, aids in equilizing the outflow of water from all the perforations in said upper wall of the pipe from one end of the pipe to the other; and said retaining means being integral also with said upper wall and is provided with a pair of inwardly projecting cams which overlie and positionally secure the respective longitudinal side edges of said unitary layer of capillary material, said retaining means being constructed to preven