Ammonium hydrogen squarate-water (3/2).

In the title compound, NH₄⁺·C₄HO₄⁻·H₂O, the hydrogen squarate anions and water molecules are arranged to form planes almost parallel to bc. The ammonium cations are located between these planes and cross-link them in the a direction by means of an extensive network of hydrogen bonds. There are two symmetry-independent sets of cations and anions. One of the hydrogen squarate anions and one of the ammonium cations are situated on a twofold axis and the H atoms of these moieties are disordered over the symmetry-related sites. [ABSTRACT FROM AUTHOR]