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The photocatalytic activity of layered perovskite-like oxides in water splitting reaction is dependent on the hydration level and species located in the interlayer slab: simple or complex cations as well as hydrogen-bonded or non-hydrogen-bonded H₂O. To study proton localization and dynamics in the HCa₂Nb₃O₁₀·<i>y</i>H₂O photocatalyst with different hydration levels (hydrated—α-form, dehydrated—<i>γ</i>-form, and intermediate—β-form), complementary Nuclear Magnetic Resonance (NMR) techniques were applied. ¹H Magic Angle Spinning NMR evidences the presence of different proton containing species in the interlayer slab depending on the hydration level. For α-form, HCa₂Nb₃O₁₀·1.6H₂O, ¹H MAS NMR spectra reveal H₃O⁺. Its molecular motion parameters were determined from ¹H spin-lattice relaxation time in the rotating frame (<i>T</i>_1ρ) using the Kohlrausch-Williams-Watts (KWW) correlation function with stretching exponent β = 0.28: <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>E</mi><mi mathvariant="normal">a</mi></msub><mo>=</mo><mn>0.210</mn><mfenced><mn>2</mn></mfenced></mrow></semantics></math></inline-formula> eV, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>τ</mi><mn>0</mn></msub><mo>=</mo><mn>9.0</mn><mfenced><mn>1</mn></mfenced><mo> </mo><mo>×</mo><mo> </mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>12</mn></mrow></msup></mrow></semantics></math></inline-formula> s. For the β-form, HCa₂Nb₃O₁₀·0.8H₂O, the only ¹H NMR line is the result of an exchange between lattice and non-hydrogen-bonded water protons. <i>T</i>_1ρ(1/<i>T</i>) indicates the presence of two characteristic points (224 and 176 K), at which proton dynamics change. The γ-form, HCa₂Nb₃O₁₀·0.1H₂O, contains bulk water and interlayer H⁺ in regular sites. ¹H NMR spectra suggest two inequivalent cation positions. The parameters of the proton motion, found within the KWW model, are as follows: <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>E</mi><mi mathvariant="normal">a</mi></msub><mo>=</mo><mn>0.217</mn><mfenced><mn>8</mn></mfenced></mrow></semantics></math></inline-formula> eV, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>τ</mi><mn>0</mn></msub><mo>=</mo><mn>8.2</mn><mfenced><mn>9</mn></mfenced><mo> </mo><mo>×</mo><mo> </mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>10</mn></mrow></msup></mrow></semantics></math></inline-formula> s.