Rand Water on Friday morning started the process of reducing flow to the three metros, Johannesburg, Tshwane and Ekurhuleni as a result of declining levels in Gauteng reservoirs.
In a statement, Rand Water said these reductions were as a consequence of higher than normal demand resulting in average storage capacity dropping below 60%.
Spokesperson Justice Mohale said some reservoirs such Brakfontein, Klipfontein, and Hartebeeshoek were currently below safe operating levels.
"Rand Water’s operating philosophy is to maintain reservoir storage levels between 60% and 80% for equitable distribution hence the measure," Mohale said.
"This is being implemented to assist with the recovery of these reservoir levels whilst managing high water consumption within the above mentioned metros."
Rand Water said it has informed all its customers of the need to reduce water consumption and use water sparingly, but did not specify when the situation would be expected back to normal.