The aim of this proposed work is to explore to behaviour of residual water (3-6 moles) found in the hydrophobic ionic liquid phases of tetrabutylphosphonium benzoate derivatives after phase separation from water. Specifically, the objectives are (i) to determine how this water is incorporated within the ionic liquid structures, whether as small pockets of ¿bulk water¿ or solvated as molecular water bound to the ionic liquid anions, and (ii) to obtain information that will help us to understand the role that different chemical functional groups within cations and anions have on the formation of water immiscible hydrophobic ionic liquids.