dl‐Arginine monohydrate at 100 K

In the title compound, C₆H₁₄N₄O₂·H₂O, the α‐amino group is neutral. The molecular side chain including the guanidinium group is not fully extended, having a near gauche–gauche conformation [χ³ = 59.0 (1)°; χ⁴ = 72.8 (1)°]. The network of hydrogen bonds stabilizing the crystal lattice includes those formed between the deprotonated and negatively charged α‐carboxyl­ate groups and the positively charged amino groups of the guanidinium group of neighbouring mol­ecules. N—H?O=C and water‐mediated N—H?O hydrogen bonds link individual mol­ecules to produce pairs of spiral motifs laterally connected by N—H?O and C—H?O hydrogen bonds.