The largely unexploited potential of small scale energy hydropower remains crucial the development of new technologies to harvest the hydraulic energy on existing facilities. In this framework, several projects have been set up by the HES-SO Valais//Wallis and the EPFL Laboratory for Hydraulic Machines. One of the developed technologies is a new hydraulic micro- turbine, for recovering the energy lost in release valves of water supply networks. One stage of the micro-turbine consists of two axial counter-rotating runners. This paper deals with the hydraulic design process of the runners for a given site, including numerical flow simulations, fabrication and performance measurements of the micro-turbine. An overview of theoretical basics, simulation settings and assumptions, simulation results and test results is given. In the last part, the design optimization process is discussed.