Non-framework cations in LTL-type zeolites can be exchanged to tune the chemical and physical properties of these materials for applications in catalysis and photo-electronics. Using highresolution X-ray diffraction and Rietveld refinement, the locations of Li, K and Cs cations and water molecules in the pores have been identified. As-synthesised K-L and partially exchanged Li and Cs-L zeolites show three distinct cation sites. With regards to cation exchange at 95°C, site B can be considered as locked and is inert to exchange with both Li + and Cs + ions, site D is deemed open and K + ions here are freely exchangeable and site C is selectively open to exchange with Cs + but not Li + . The occupancy of site C seems to be favoured by larger cations such as Cs + , where the instability of Li + is likely a result of its small cationic radius, long bond lengths and a low interaction energy with the framework. Refinement of water positions shows that water molecules are partitioned into two distinct layers-a cation-stabilised cluster and a hydrogen-bonded layer. This is in agreement with the analogous gallosilicate reported by Lee. . Exchange of K + for Cs + or Li + induces the redistribution of water among these layers, suggesting that their arrangement is dictated by the stabilising effect and steric of the extra-framework cation. The free access diameter of the 12R channel, cation locations and water distribution in LTL-type zeolites can be tuned by altering the size of the exchanging cations. In addition to steric effects, cations with different ionic radii have different charge densities which alters the electric field within the pore systems. This not only has important implications for the selective adsorption of guest molecules, but will also affect their diffusion and stability within the channels. By selecting the appropriate non-framework cation, the LTL-framework can be finely tuned to enhance selectivity and host-guest interactions for applications in catalysis, molecular sieving, and zeolite-dye optoelectronic materials.