Sodium hydrogensquarate monohydrate

In the title compound, sodium 2-hydr­oxy-3,4-dioxocyclo­but-1-en-1-olate monohydrate, Na+·C4HO4−·H2O, the Na atom is six-coordinated by the O atoms from four hydrogensquarate anions and two water mol­ecules. The three-dimensional packing is stabilized by a system of hydrogen bonds.