We report here on the moisture and water stability of the promising Na-ion anode material Na2Ti3O7. Spontaneous Na+/H+ exchange is detected by PXRD after air exposure, forming solid solution compounds of the form Na2−xHxTi3O7 (0 < x < 2). By controlled ion exchange in aqueous solution two mixed compositions are prepared and their composition and structure are characterized with a panel of techniques. Both mixed compositions crystallize in C2/m space group like H2Ti3O7, and therefore Na+/H+ exchange is found to involve a structural transition from AA stacking of [TiO6] layers to AB stacking sequence. The electrochemical behaviour of the mixed compositions vs. Na+/Na is studied as well as that of an electrode of pure Na2Ti3O7 prepared in water media. The water-processed electrode is shown to exhibit a superior cycling stability and therefore the results obtained highlight the potential of Na2Ti3O7 as a green, low cost anode material for NIBs.