In the structure of the title salt, (NH(4))(C(8)H(20)N)(2)[Fe(CN)(6)].3H2O, the O atom of one of the water molecules shares its crystallographic site with the N atom of the ammonium cation in a 1:1 ratio. The second O atom from the two crystallographically independent water molecules is disordered over two positions separated by 0.551 (1) A. The water molecules and ammonium cations form tetrameric hydrogen-bonded units that, along with the complex anion, form the hydrophilic part of the structure. The hydrophobic part of the structure, represented by the tetraethylammonium cation, is located in cube-like cavities of the hydrophilic framework.