Waterbucks belong to a subfamily of bovids called Reduncinae, which also includes kobs, reedbucks, and lechwes. Waterbucks are the largest animals in this sub-family, with males weighing more than 500 lb (227 kg) and standing more than 4 ft (1.2 m) at the shoulders. Female waterbucks are slightly smaller. Only male waterbucks have horns, which are V-shaped, tapered, ridged, and curve backward, then slightly forward at the tips.
Two subspecies of waterbuck are recognized: the common waterbuck Kobus ellipsiprymnus ellipsiprymaus and the defassa waterbuck K. e. defassa. Some scientists consider the defassa waterbuck to be a separate species. One distinguishing marking between the two is their coloration. Defassa waterbucks are silvery-gray or reddish to dark brown with a streak of white on their rump. Common waterbucks have a distinctive white ring around the rump, the lower half of the legs are black, and they have white markings at the throat, an eyebrow line, and a white snout. Males tend to darken with age.
Waterbucks lack scent glands, but possess a greasy coat with skin glands that secrete a smelly, musk odor that can be detected as far away as 1600 ft (488 m) away. The greasy, shaggy coat serves to protect waterbucks from the damp habitats. Waterbucks do not run rapidly, moving mostly at a trot.