The filling of water mains represents a type of transient flow which follows some maintenance procedures or when the pipelines are commissioned. This process is performed carefully in order to avoid the formation of air pockets, which can cause dangerously high pressures in the conduits and also reduction of their conveyance capacity should pockets remain entrapped. Numerical modeling is a useful tool for these flows as it may anticipate operational issues during filling events, and examples of such models are presented by Liou e Hunt (1996), Izquierdo et al. (1999) and Vasconcelos (2007). Yet, some of the proposed models may have limitations on their applicability as some hypothesis used in their formulations may not be valid in many practical situations. This work has the objective to develop a simple numerical model for the simulation of gradual filling of water mains based on more realistic hypothesis regarding the shape of the pressurization front and the air pressurization process. For that purpose, the model couples an unsteady open-channel solver with a rigid-column model for the pressurized portion of the flow, considering also for the pressurization of entrapped air pockets. Different configurations are simulated in the model, and the effects of different air ventilation and inflow rates are assessed. Even though this research is a work in progress as the model is undergoing calibration based on experimental data, it has the potential to become a useful tool for the simulation and design of pipe-filling flows.