Three new water-responsive luminescent lanthanide-free polyoxometalate (Ln-free POM) materials Na₇[SbW₆O₂₄], K₅Na₂[SbW₆O₂₄] and K₇[SbW₆O₂₄] were prepared by thermally dehydrating two known compounds Na₇[SbW₆O₂₄]·16H₂O and K₅Na₂[SbW₆O₂₄]·12H₂O, and a new one K₇[SbW₆O₂₄]·6H₂O. The isostructural anhydrous phases have been fully characterized by a combination of techniques (high temperature powder X-ray diffraction (HT-PXRD), thermal analyses, scanning electron microscopy (SEM), and FT-IR, FT-Raman, UV-vis and photoluminescence (PL) spectroscopies), and their structures have been solved from ab initio powder X-ray diffraction determination. The PL properties of these materials are reversibly tunable by controlling their hydration degree. The three hydrated compounds are barely luminescent or nonluminescent at room temperature because water molecules promote the non-radiative deactivation processes from the emitting levels of the [SbW₆O₂₄]⁷⁻ unit. However, the anhydrous phases show remarkable PL enhancement. The PL quantum yields vary with the nature of the alkali ions, and Na₇[SbW₆O₂₄] exhibits the best performance of this series. These materials also exhibit highly efficient turn-off vapoluminescence properties upon exposure to a humid atmosphere. They are fully converted into their parent hydrates, resulting in strong and complete PL quenching effects. The rehydration kinetics are much faster for K⁺-containing materials, which could be interpreted taking into account the structural filiations between anhydrous and hydrated compounds. Finally, the complete regeneration of PL-active anhydrous phases can be achieved by simple thermal dehydration.