The Westbury area, a suburb of the city of Johannesburg, is characterized by a very old pipe network, high water losses as well as high operating and maintenance costs. Consequently, a network rehabilitation project was proposed for the area, with an overall aim of improving network efficiency through pipe replacement. This proposal led to the current study with the key objective of determining the impact that pipe roughness has on network performance. In order to achieve this goal, a model of the area was obtained and analysed as a gravity-fed network containing 490 pipes, 407 junctions and 5 reservoirs. From the study, key findings reveal that the smoother the internal pipe walls, the higher the pressure at which demand is met. In addition, power delivered to consumers increases with internal pipe smoothness, and power dissipated in the network increases with pipe roughness. On the other hand, the relationship between roughness and leakage is inconclusive.