The objective of the end-of-studies internship carried out within Urban-Water-Process department of Egis Montpellier was to create a tool for the computation of the carbon footprint of water-treatment processes. The existing materials and methods describing how to calculate a carbon footprint for urban wastewater processing were studied in order to define the scope, scenarios, and functionalities that needed to be covered by the tool. A database, calculation and results sheets have been created which enable the calculation of the carbon footprint of a WWTP for its operating phase. The tool makes it possible to calculate the carbon footprint of WWTP processes at the master plan stage, proposed WWTP systems, and existing WWTP plants.