Unique to the Middle Sepik River region of northeast New Guinea, water drums consist of a hollow, hourglass-shaped cylinder of wood with one or two handles projecting from the top. To play the instrument, two men grasp the handle or handles and strike the drum vertically against the surface of a body of water. As the lower end of the drum breaks the surface, it produces a thudding sound.

Among the Iatmul people, who created the example seen here, water drums are secret instruments, kept hidden from women and children, which are played in pairs by men as part of male initiation ceremonies. The watery thump of the drum is said to simulate the sound of the initiates being swallowed by a supernatural crocodile, who later spits them back out, their bodies covered by the marks of its teeth. In actuality, the "teeth marks" are the numerous cuts made by the initiators on the bodies of the novices as part of the ceremony, which later heal into the permanent scarification patterns that mark them as initiated men. The image of the crocodile that adorns this water drum, its tail thickened to form the handle, is almost certainly a visual reference to the supernatural crocodile whose actions form the core of the initiation ceremony in which the instrument is used.