Rand Water is implementing stage two water supply restrictions.
The City of Johannesburg said this was due to increased usage in the current heatwave, with Rand Water concerned that this is unsustainable.
The city confirmed that usage had risen at an “alarming rate”.
Johannesburg Water has begun throttling reservoirs by between 20% to 40% in line with the restrictions imposed by Rand Water.
Another heatwave is expected this weekend, and the city has appealed to customers to use water sparingly.
Rand Water has called a briefing for Friday, at which it will share how it intends “to address the current water demand issues and their immediate impact on consumers”.
The city said earlier this week that the Vaal Dam's levels had fallen below 50% for the first time in nearly three years. Around the same time last year, the dam was more than 86% full.
