Rand Water says it is waiting for a detailed technical report from Johannesburg's City Power after a fire broke out at Eikenhof Pumping Station on Monday.
Spokesperson Justice Mohale said on Thursday that a City Power technical representative had informed the utility that the incident was linked to a tap changer failure at the station.
"Rand Water and City Power have it on record that City Power has been experiencing numerous transformer problems, including the tap changer," Mohale said in a statement.
The fire, which broke out on Monday night, affected the pump station which houses a transformer linked to Rand Water.
On Tuesday, City Power said it suspected that the cause of the explosion at the pumping station was a "result of a deliberate act of sabotage".
City of Johannesburg Mayor Herman Mashaba said in a statement that a video had emerged which proved that the fire had originated outside the transformer at the substation.
Mashaba said the transformer appeared to have been "maliciously damaged so that it would leak oil onto the fire".
Johannesburg Water was forced to place water tankers at locations across the city to assist residents after they were left without electricity and others were without water.
Areas that were affected included the greater Roodepoort, Randburg, Langlaagte, Southdale and Soweto. Water has since been restored to most parts of the city, Johannesburg Water communications officer Eleanor Mavimbela said on Thursday. "We are currently working on restoring a small portion that is still without water and we're adding more water tankers in those areas," Mavimbela added in a statement.