Average values of k₁, k₂, and β fitted from inactivation levels are presented in Table 2. The degree of tailing is captured in the β term. As expected, the percentage of UV-resistant microorganism (β) is significantly different in DC raw and pre-UV with values of 64 and 19%, respectively (p < 0.001). DC raw samples had higher organic carbon levels and average turbidity compared to DC pre-UV (DC Raw TOC = 9.19 mg/L, turbidity = 3.52 NTU; DC pre-UV TOC = 4.30 mg/L, turbidity = 0.51 NTU). This suggests that treatment in DCWTP (coagulation + flocculation + DAF system) resulted in a reduction of conditions that cause UV-resistance. The PSD was also measured to explore possible relationships between size and the obtained results. Two peaks were observed in PSD by volume figures of DC raw water at 0.69 and 5.17 μm, while in DC pre-UV samples, only one peak at 4.95 μm was reported. Data suggested that the treatment applied to DC raw removed the portion of particles smaller than 1 μm. The remaining portion of particles within the size range of 2–6 μm would carry over to the disinfection stage. It has been found by previous studies that UV disinfection efficacy is linked to particle size (Winward et al. 2008). Therefore, it is possible that the DAF process removes particulates and small colloids that could interfere with disinfection and result in better UV disinfection and a lower level of tailing.