It could take up to three days, for water systems to recover.
This follows an electricity outage at the Zuikerbosch water treatment pump, on Wednesday.
Johannesburg Water said although power was restored and Rand Water resumed pumping, systems in Sandton and Midrand continue to receive low supply.
The local water entity also said reservoirs are low in the Sandton systems, Illovo, Midrand, Grand Central, President Park and Tower.
Picture: Supplied