Figure illustrates the refined water sites in K-L that are fractionally occupied. The O-O distances suggest that water molecules form discrete, hydrogen-bonded layers and cation-stabilised water clusters, in agreement with those nanostructures in the analogous gallosilicate reported by Lee et al. . Cation exchange can be utilised as a tool to manipulate the geometries of the water nanostructures within the 1-D channel system of LTL-type zeolites. Water content fluctuates with the nature of the cation at site D. This could be particularly useful for host-guest systems which depend on variable degrees of hydrogen bonding for stabilisation. Table shows that the overall water content of the channel decreases upon exchange of K + ions with both Li + and Cs + ions. For Cs-L, this can be rationalised by the decrease in free volume available to accommodate water molecules. Large Cs + ions are further displaced into the centre of channel and there is a drastic reduction in the number of water molecules per unit-cell that can be supported in a cation-stabilised cluster. Water content also decreases when K + is partially exchanged for Li + . Again, the decrease in water content can be accounted for by the position of the cations at site D. Smaller Li + ions are displaced towards the channel walls and cannot interact as efficiently with water molecules to form cation clusters. Furthermore, the reduced K + occupancy at site D means that there is also a reduction in stabilising interactions from K + ions with water in the cation-stabilised water cluster.