An innovated waterjet concept led to a milestone in impeller design field. Yet, incompatibilities issues with numerical model brought designer to give up. Present work solves these issues and leads up to a new original design method. Impeller preliminary design procedure and it numerical model are first surveyed. A careful appraisal of logical frameworks underlying both models reveals key inconsistencies. As far as theoretical model is concerned, self-contradictions between main assumptions are found. These shortcomings are also remarked through numerical model results scrutiny. Further, a major lack in numerical model settings is recognized. Both models are then improved. Classic design method is refined with diffuser conservation principles and aeronautics expertise implementation. Results are then exploited to revise numerical model settings. Thus, an impeller redesign is achieved and results obtained are discussed. Finally, these are compared with initial ones. Significant improvements as concern models representativeness are achieved. An innovative design procedure well suited for a performing waterjet is thus outlined.