In the title structure, C(7)H(9)N(3)O(2)·H(2)O, there are two formula units in the asymmetric unit. The mol-ecule is a zwitterion, containing a quaternary N atom and a deprotonated carboxyl group, with C-O distances in the range 1.256 (2)-1.266 (3) Å. The two independent mol-ecules form a hydrogen-bonded R(2) (2)(16) dimer about an approximate inversion center via N-H⋯O hydrogen bonds, with N⋯O distances of 2.766 (2) and 2.888 (2) Å. O-H⋯O hydro-gen bonds involving the water mol-ecules and additional N-H⋯O hydrogen bonds link these dimers, forming double chains.