Traditional water channels (Aflaj) feature pedestrian alleyways that offer passive cooling potential for hot, arid climates; however, the combined microclimatic effects of water channels within alleyways remain inadequately studied. This study employs CFD simulations using STAR-CCM+ to investigate the thermal comfort implications of water channels across 14 alleyway configurations and 27 environmental conditions, and at three simulation hours (12, 15, and 20), totaling 1134 cases. The numerical model was validated against wind-tunnel experiments and incorporates multiphase fluid-film evaporation modeling. The results demonstrated that narrow alleyways reduce daytime temperatures by 4.8 degrees C compared with the same alleyway configuration without active water flow, with humidity exceeding 40% in deep canyons. Three-way ANOVA reveals wind speed as the dominant factor governing channel cooling effectiveness (eta 2p ranging from 0.49 to 0.75), while temperature and humidity effects vary by geometry and time of day. Despite elevated humidity, thermal comfort improved in narrow configurations, with PET reductions of up to 2.40 degrees C and a 87.9% increase in comfort for the optimal design at peak daytime conditions. Wide alleyways show minimal cooling benefit, and in some multiple-channel configurations, thermal comfort worsens due to solar radiation absorbed and reradiated by channel walls. The alleyway aspect ratio, rather than the water surface area, is the most significant factor determining the effectiveness of evaporative cooling. This conclusion provides critical guidance for designing sustainable pedestrian spaces in hot and arid regions.