The title compound, C(10)H(11)N(2)O(2)P·H(2)O, contains a tetra-coordinate penta-valent P atom. The phosphinate group plays a predominant role in the cohesion of the crystal structure by forming chains along the b axis via inter-molecular C-H⋯O hydrogen bonds. These chains are connected by O-H⋯O and N-H⋯O hydrogen bonding involving the lattice water.