It is a great pleasure to share you the Abstract Book, which contains all presentations that have been included in the programme of the MonGOS International Conference: Water and Sewage in the Circular Economy Model. In nine sessions of the MonGOS International Conference, Practitioners and Theoreticians presented works related to the implementation of CE in the sector, in two key areas: sustainable management of primary resources (water, raw materials, energy) and, circular management of secondary resources (waste generated in the sector, including sewage, sewage sludge, and other waste).