Rand Water has confirmed that its B16 pipeline, which runs from Zuikerbosch to Slangfontein, was vandalised on Tuesday evening.
The two 300mm damaged scours caused a serious leak.
"In order to repair these valves, Rand Water has had to shut down the pipeline. By shutting down the line, water supply to its Brakpan reservoirs was reduced by 200Ml/d," it said in a statement.
Rand Water added that the reduction was slowly depleting the Brakpan reservoir levels.
"If these reservoir levels run empty, supply interruptions can be expected in Tshakane, Lesedi, Nigel, Marievale, North Boundary and Duduza."
The company added the repairs were expected to be completed by Wednesday evening .