Recent Mars Global Surveyor Thermal Emission Spectrometer (TES) observations have shown the effects of a global dust storm on the water cycle on Mars. Simulations using a Mars General Circulation Model were conducted to assess the influence of an arbitrary global dust storm on the modelled water cycle. Further, the effects of an adsorbing regolith during the dust storm were examined. Both with an active and a passive regolith the water cycle is substantially affected during the course of the dust storm, but returns to ambient conditions soon after the storm has abated. Differences between the simulations do exist, especially in the southern hemisphere during summer. When comparing the simulations with observations both the active and passive regolith simulations fail to fully replicate the general trends observed by TES. However, the actions of an adsorbing regolith appear to result in a water cycle more closely resembling the observations.