EPANET is free US EPA software that models flows, pressures and water quality in pressurised drinking water pipe networks over time.
EPANET is software from the US Environmental Protection Agency (US EPA) for modelling drinking water distribution systems. It is free and open source, and its calculation engine is used inside many other network tools. Utilities and engineers use it to check pressures, size pipes and pumps, plan operations and follow chlorine or water age through the network. EPANET represents a network as nodes and links. Nodes are junctions with water demand, tanks and reservoirs. Links are pipes, pumps and valves. For each time step the model solves mass balance at every node and energy balance along every link at the same time. Head loss in pipes can use the Hazen-Williams, Darcy-Weisbach or Chezy-Manning formula. This is repeated over an extended period, such as 24 hours or a week, with demands following daily patterns and tank levels changing. A water quality solver then moves substances through the pipes, with options for chlorine decay, water age and tracing water from a source. Inputs are the network layout, node elevations, demands and demand patterns, pipe length, diameter and roughness, pump curves, valve settings, tank sizes and control rules. Outputs are pressure, head and quality at every node, and flow, velocity and head loss in every link, at each time step. For example, a utility can test whether a new housing area can be served without pressures dropping below its target at peak hour, and compare a new main against a booster pump. EPANET is free, fast and accepted as a reference engine. A programmer toolkit lets other software call it directly. Its limits: it does not model surge or water hammer, results depend heavily on how demands are assigned to nodes, and a model must be calibrated to field pressures and flows before it is trusted.