EPANET is a public domain, water distribution system modeling software package created by the US Environmental Protection Agency (EPA). It uses a mathematical engine, the EPANET engine, for solving hydraulic equations and calculating pressures and flows across the network.
It is the engine used by most hydraulic modeling applications such as InfoWater (Pro), WaterGEMS/WaterCAD, Fluidit Water, and, of course, Qatium.
Qatium, on the other hand, is an open and collaborative water management platform that allows you to build a digital replica of your network within minutes and provides you with all the necessary tools to optimize its performance.