The title tetracyclic diterpenoid, 10,13,16,17-tetra­hydroxy-9-methyl-15-oxo-20-norkaurane-18,10-carbolactone hemihydrate, C₂₀H₂₈O₆·0.5H₂O, is a plant metabolite from Parinari sprucei, part of the Venezuelan Amazon flora. The asymmetric unit consists of two nearly identical mol­ecules of the diterpenoid and one mol­ecule of water. Some of the geometric parameters reflect steric strain in the mol­ecule. The extended structure is characterized by hydrogen bonds and weaker hydrogen-mediated interactions, which involve all of the hydroxy groups and propagate in sheets that coincide with the (002) family of planes. The water mol­ecule acts as a double hydrogen-bond donor and single acceptor and thus plays a critical role in the pattern of intermolecular interactions.