Epanet water quality simulator uses a Lagrange time-based approach to track the fate of discrete parcels of water as they move along the pipes and mix at the junctions between time steps of fixed length. These water quality time steps are typically much shorter than the hydraulic time step. (e.g. minutes rather than hours) to accommodate the short travel times that can occur within pipes. However, as with hydraulics, results are only reported at the end of each user-specified reporting time interval.
The following topics provide more detail on modeling water quality with EPANET: