With the adoption of the European Water Framework Directive focus on pollutant emission has been shifted to the receiving water itself. For the WFD implementation, modeling of the integrated urban wastewater system (IUWS) will be needed and has many advantages for planners, operators and managers.

The IUWS is a highly complex system including at the same time physical, chemical and biological processes. Examples are the rainwater runoff from pervious or impervious surfaces and domestic or industrial wastewaters, altogether transported to a wastewater treatment plant (WWTP), treatment of the combined sewage at the WWTP, discharges of these waters after treatment, and/or via combined sewer overflows (CSOs) during rain events, and the receiving water itself. Having all these different parameters playing a role and given the infinite amount of data, it is difficult to analyze and predict the evolution in time of the IUWS.

WEST allows users to represent dynamical processes in a mathematical model, enabling simulations and virtual experiments. WEST is a tool to predict situations, give answers to precise questions and improve ecological and financial efficiency of the IUWS.