Hydrophilic ions in oil phase tend to be hydrated in the presence of trace water and form hydrated clusters. The present paper elucidates the equilibrium size distribution of hydrated ion clusters and the microscopic rates of adsorption and desorption of water with the help of molecular dynamics simulations. The size distribution is derived from reversible work of hydration, which is nearly constant over the hydration number except for small clusters. The intrinsic rate constants of adsorption and desorption are evaluated to be in several psec order after correcting the diffusion. The microscopic hydration properties of ions in the oil phase play key roles in chemical reactions involving both hydrophilic and hydrophobic reactants as well as in the transport and reactivity of the ions in oil phase and at the water-oil interface.