The paper presents the results of studies on local resistance coefficients (ζ). The study used pipe aerators with filling made according to the Polish patent PL235924. The hydraulic investigations were performed in real working conditions of a water treatment plant in a testing rig built in the Scientific and Research Water Station of the Warsaw University of Life Sciences (SGGW). The investigation encompassed two plastic pipe aerators of an internal diameter 101.6 and 147.6 mm with steel Białecki rings of 12 and 25 mm in diameter. Measurements of pressure difference (Δp) in the investigated aerators were performed at volumetric water flows ( Q) selected from the range 2–20 m ³∙h ^–1 with the interval 2 m ³∙s ^–1. The values of ζ were determined according to the PN-EN 1267:2012 standard. The investigation showed that the ζ depends both on an internal diameter of the plastic pipe aerator and the diameter of Białecki steel rings. The values of ζ increase with a decrease of the internal diameter of the pipe aerator and a decrease of the ring diameter.