The title compound, C18H24N2O4·H2O {systematic name: (1aR,7aS,8R,10aS,10bS,E)-5-hy-droxy-methyl-8-[(1H-imidazol-1-yl)meth-yl]-1a-methyl-2,3,6,7,7a,8,10a,10b-octa-hydro-oxireno[2',3':9,10]cyclo-deca-[1,2-b]furan-9(1aH)-one monohydrate}, an imidazole derivative of melampomagnolide B was synthesized under Michael addition conditions. The mol-ecule is built up from fused ten-, five- (lactone) and three-membered (epoxide) rings. The inter-nal double bond of the ten-membered ring identifies it as the cis or E isomer. The lactone ring has an envelope-type conformation, with the (chiral) C atom opposite the lactone O atoms as the flap atom. In the crystal, O-H⋯O, O-H⋯N and weak C-H⋯O hydrogen bonds link the mol-ecules (along with water) into sheets parallel to the bc plane.