In the monohydrate of 2-amino-8-(2-deoxy-α-D-erythro-pento­furan­osyl)-8H-imidazo­[1,2-a]­[1,3,5]­triazin-4-one, C₁₀H₁₃N₅O₄·H₂O, denoted (I) or αZ_d, the conformation of the N-gly­cosyl­ic bond is in the high-anti range [χ = 87.5 (3)°]. The 2′-deoxy­ribo­furan­ose moiety adopts a C2′-endo,C3′-exo(^2′T_3′) sugar puckering (S-type sugar) and the conformation at the C4′—C5′ bond is −sc (trans).