This book presents the automated pre-dimensioning of units of a Water Treatment Plant (WTP) with the use of spreadsheet resources allied to the supplements of Solver and VBA contained in the Microsoft Excel environment, thus aiming at the initial arrangement of the WTP. In the sizing stage, the conventional WTP consisted of a rapid mixing unit with Parshall flume, hydraulic flocculation unit with vertical chicanes, decantation unit with rectangular decanter of horizontal flow, and a rapid filtration unit. It was observed that in the pre-dimensioning, it was possible to solve the problems in order to meet the parameters required by the standards in force and the bibliographies, leaving the WTP arrangement consisting of a fast mixing unit, a flocculator, four decanters and four filters. In parallel, 3D modeling was also used to help visualize the hydraulic dimensioning and the construction of the initial arrangement of the proposed system. It was concluded that the resources used in this study proved to be another tool to assist designers in the conception stage of WTP projects.