Water was being restored to large parts of northern Johannesburg on Wednesday, after an unknown problem had left residents without water since Tuesday.
Areas affected were Bryanston, Epsom Downs, Palmlands, Douglasdale, Fourways, Lonehill, Magaliessig and surrounds.
Johannesburg Water tweeted on Wednesday midday: "JW can confirm that service is being restored now and customers will have water later this afternoon. The reservoir has not yet reached capacity and the investigation still continues."
Several Twitter users reported that water had been restored.
Johannesburg Water urged residents to use water sparingly, as the reservoir was building capacity, and to report all leaks to its call centre.
Earlier on Wednesday, Johannesburg Water tweeted that it was experiencing "challenges with our Bryanston reservoirs. The reservoir levels are low and, therefore, we had to close the outlet."
Johannesburg Water spokesperson Isaac Dhludhlu told News24 on Wednesday morning that the cause of the problem had not yet been determined.
"We are still investigating," he said. "The water that goes into the reservoir is not enough, so we have lost pressure and capacity in the reservoir."
Johannesburg Water had made water tankers available at Nicolway Shopping Centre, Epsom Downs, Douglasdale, Fourways/Fourways Mall, Pineslopes Shopping Centre, Leopard Frog and Lonehill Boulevard.
Last month, a substation that provides electricity to the Rand Water infrastructure which pumps water to approximately 40% of Johannesburg, as well as parts of the West Rand and Rustenburg, caught fire in an apparent act of sabotage, and water supply to many suburbs was interrupted.
City Power spokesperson Isaac Mangena told News24 at the time that the damage was so severe that, under normal circumstances, it would have taken at least 72 hours to repair.
Supply was, however, restored within 32 hours.