Wau was initially established as a zariba (fortified base) by slave-traders in the 19th century. During the time of condominium rule, the city became an administrative center.
Burr and Collins in 1994 described Wau: as follows:
No one has ever been “at home” in Wau. It is surrounded by a host of disorganized and diverse peoples . . . It was and remains a town belonging to no single ethnic group, deriving its importance only from its position as a commercial and administrative center . . . Located in the midst of the vast Nilotic plain hundreds of miles from nowhere, it was miserable under the best of circumstances . . .
In 2008, Wau was the third-largest city in South Sudan, by population, behind Juba the capital and Malakal, in Upper Nile State. At that time, the estimated population of the city of Wau was about 128,100. In 2011, the city's population was estimated at about 151,320.