7‐Methoxy‐2,3‐dioxo‐1,4‐dihydroquinoxalin‐6‐aminium chloride monohydrate

Single crystals of the title compound, C₉H₁₀N₃O₃⁺·Cl^?·H₂O, were obtained by recrystallization from hydrochloric acid. The cations stack along the crystallographic a direction. The 2,3‐dioxo‐1,4‐dihydroquinoxaline group shows a significant deviation from planarity r.m.s. deviation from the best plane = 0.063 (2) Å]. Hydrogen bonding links the cations, chloride anions and water molecules to form an extended three‐dimensional architecture.