Abstract This paper reports the optimization and the characterization of a 4 cm diameter water flow energy harvester inserted in pipes. In this work, a test-bench has been implemented to measure the harvester’s electrical output powers, rotation frequencies and pressure losses. Furthermore, long-term tests have been carried out in a district heating and cooling system (DHCS) in order to validate its operation in a real environment. Output powers up to 490mW @ 9 m3.h−1 are reported with a mean output power of 5mW in real conditions (Montpellier’s DHCS in France). The pressure losses induced by the turbine and the energy extraction remains lower than 50 mbars which is among the lowest in the state of the art.