A new polymorph of lithium zinc phosphate hydrate, β-LiZnPO₄·H₂O, has been obtained by hydrothermal synthesis, and its crystal structure and thermal transformation investigated. The crystal structure can be viewed as a framework structure built from PO₄ and ZnO₄ tetrahedra with LiO₄ tetrahedra and water molecules placed in eight-ring channels; β-LiZnPO₄·H₂O is apparently the only member of the zeolite ABW group of materials crystallising in space group P2₁ab. It has a doubled b axis compared to a known phase of LiZnPO₄·H₂O. The ³¹P MAS NMR spectrum showed two signals; δ 6.94(2) and 7.88(2). The known phase of LiZnPO₄·H₂O transforms into β-LiZnPO₄·H₂O after treatment in 0.9 M LiNO₃ (aq) at 80 °C and 10 kbar for 20 h. A mechanism for the pressure-induced displacive phase transition is proposed. Dry or hydrothermal heating of β-LiZnPO₄·H₂O at >100 °C gave δ_I-LiZnPO₄. The enthalpy change for the dehydration with a maximum at 219(2) °C was determined to be ΔH = 43(6) kJ mol^–1, using differential scanning calorimetry.