Clean water provision is one of the greatest challenges for the human population of the 21st century. One way to overcome this problem is through the desalinisation of seawater using renewable energy solutions to minimise fossil fuel consumption. However, the cost of producing clean water with renewable energy technology is more expensive when compared to conventional technology. In this paper we present a numerically study of the use of tidal stream energy to desalinate water. The proposed solution incorporates the use of an integrated f luid power transmission systems where the desalination process occurs within the tidal turbine converter itself without intermediate electrical conversion. The numerical model is developed to incorporate the coupling between the tidal stream rotor hydrodynamics and the behaviour of the desalination system when subject to an average f low speed of 1.5 m/s and three turbulence intensity levels of 6.5%, 12% and 17.5%. Time-domain simulations of the simplified coupled system show the dynamic response of the relevant operating parameters, such as torques, rotational speed, pressures as well as the amount of fresh water production. It was found that an average cumulative permeate of 6.8 m3 could be obtained from a 10 m tidal stream turbine for a ten minute operation. When the turbine operated at the lowest turbulence intensity levels, there was a increase of 11% more fresh water production compared to the average cumulative permeate output and when the study was performed at the highest turbulence intensities, the fresh water production decreased by almost 7%.