In this paper, the model of fluid mixing in double T-junctions is described in detail. Accordingly, a laboratory experiment was also performed and described. The experiment consisted of a series of experiments with different input ratios and ranges between the two T-junctions. Also, the experiment was modeled numerically. Flow analysis and pipeline losses in system were computed numerically using numerical software AFT Fathom. Also, in this paper, all hydraulic elements and sensors required for the experiment were described in detail. There are also given experimental and numerical results of fluid mixing for three different ranges of Tjunctions and visually displayed flow diagrams. The methods of contaminations of the systems and the mixing theory in junctions itself are described in detail. With this paper, knowing the mixing ratios in T-junctions, it is possible to precisely determine the part of the pipeline in which mixing and dispersion of the contaminants occurs. Therefore, it is possible to quickly and effectively solve the pollution problem in water supply networks.