K6.16Na0.16Ca0.07Mg0.03(H2O)19.2|[Al6.45Si29.55O72] (space group C2/m, a = 17.6490(3) Å, b = 17.9982(2) Å, c = 7.39329(12) Å, β = 116.0655(19)°, V = 2109.63(5) Å3, Z = 1) is studied by the single crystal X-ray diffraction analysis under ambient conditions and also upon compression to 4 GPa in penetrating (water-containing) and non-penetrating (paraffin) media. Compression of Ksubstituted clinoptillolite in a water:ethanol (1:1) mixture results in its additional hydration: inclusion of 2.2 additional H2O molecules into the structure at the initial stage. Upon further compression the H2O concentration increases by two molecules. This is caused by additional occupancy of partially vacant H2O sites. The cation environment practically does not change during overhydration. Changes in the coordination polyhedra of cations during compression in paraffin are reduced to a small (0.02-0.1 Å) decrease in bond lengths. Distinctions in the degree of hydration of the K-form upon compression in penetrating and non-penetrating media are manifested in the features of the compressibility of the compound.