In this chapter we will develop an algorithm to hydrologically and structurally calculate a PHIT so it can be preliminarily designed. To do this, the file content, bibliography, Basic HPP Project and Authorization or Concession Agreements from ANEEL must all be available to the PT, no to mention the studies developed in the previous chapters. Using this documentation, the PT will establish the determine the input data, which must be stored in the computer’s memory banks so that each result can be obtained as predicted by the designers and programmers. The algorithm will detail the applicable steps and which any established alternatives to maintain continuity, so the results give possible or best alternatives within the corresponding hypotheses. Once the algorithm is validated, it can be used both in PHIT models and in prototypes, particularly as a foundation for conducting the Basic, Executive, and Manufacturing Projects, along with the test programs for the laboratory, factory, or site.