Drilled impellers represent an alternative approach to the construction of impellers of centrifugal pumps, operating within the specific speed of nq < 10. Their construction is very simple and can be achieved by employing machining methods. This paper presents the impact of the basic construction parameters of drilled impellers on the efficiency of the process of energy transfer into liquid. The main focus is on testing the efficacy of using additional side holes. The main testing method involves computational fluid dynamics (CFD) simulations. The selected impeller constructions are made with the SLS (rapid prototyping) method and tested with a test rig. The paper presents a comparison of numerical and experimental results. Based on the obtained results the author makes recommendations on the construction of drilled impellers