The integration of seawater desalination and wind energy technologies has allowed for the development of a directly wind-driven desalination system, with the potential to address freshwater scarcity issues without contributing to CO2 emissions. The system described in this manuscript consists of a wind turbine rotor, which employs a hydraulic transmission to directly pressurise seawater into a reverse osmosis desalination plant and a Pelton turbine generator. After building and commissioning of a 44 m hydraulic wind turbine prototype in the port of Rotterdam in the Netherlands, an experimental campaign was conducted to evaluate the operational range and performance of the hydraulic system. A combination of hardware-in-the-loop tests where used to get insight into the behaviour of the integrated system. The control philosophies used for automatic operation and safety of the system are compared and discussed, as well as the system's behaviour in response to different wind conditions using dummy elements to replace the desalination module. Technical challenges and achievements of commissioning and testing the system are also described, along with lessons learned.