Pumps are hydraulic machines with the widest industrial applications; hence the need for a detailed study of the influence of cavitation on their performance. This chapter presents the point of view of a user whose objectives may vary with the intended application. It also presents the procedures of extrapolation of the performance under cavitation conditions of similar pumps. They are, in fact, rotary machines equipped with blades. The essential problem in the case of turbines is the requirement of good output and no eroding cavitation. Numerical models are available with which performance including the pressure distribution on individual blades can be predicted with a good degree of accuracy. Cavitation on propellers appears in different forms: travelling bubble, attached on the blade, tip vortex, hub cavitation at the root of blades and vortex cavitation along the axis of the machine.