The areas of Delft, Epping, Brooklyn, Woodstock and Salt River are in line to have their water supply disrupted and new water pressure management technology installed to bring water usage down.
The City said it would implement further pressure management testing to bring collective usage down to 450 million litres a day.
This requires individual water users to stay within a daily allocation of 50 litres to avert Day Zero.
Work was scheduled for Delft, Epping Industrial 1 and 2 areas, Woodstock and Salt River last night, and work is scheduled in the Brooklyn area tonight between 8pm and 4am.
Other areas will be informed of supply disruptions in due course, the City said.
Affected areas have been asked to keep taps closed and to not stockpile large volumes of municipal water as the service interruptions are not expected to be in effect for long periods.
City director for water and sanitation Peter Flower said not only does pressure management generally lower consumption by reducing the rate at which water flows to properties, it also reduces the risk of leaks and pipe bursts by better ensuring that pressure remains within levels that reduce stress on the infrastructure.
“We have identified at least 25 areas that could benefit from this technology.
"Further implementation will be rolled out over the next few months and contractors have been brought in to speed up the programme,” said Flower.
In line with Level 6 drought measures, the February 2018 water and sanitation accounts will reflect a tariff increase.
Meanwhile, organisers of the Old Mutual Two Oceans Marathon (OMTOM) are
working around the clock to ensure the 49th edition of the event is fully aligned with plans to avert Day Zero.
No municipal water will be used at any of the OMTOM events, as water for race day has been sourced from the Newlands Spring with an allocated and approved dispensation from relevant stakeholders, including the Department of Water and Sanitation.
The purified spring water will be distributed to all participants via sachets and other systems. Some runners will use hydration packs to fill up at the start of the race instead of using their daily allowance, while refill stations for hydration packs will be positioned along the ultra marathon route.
It has also been agreed that no shower facilities will be provided at the finish line. Chemical toilets brought to the various OMTOM sites will use only certified recycled water. UCT is closing all taps at the finish area, while the fixed showers at UCT will be inaccessible.
Two Oceans Marathon non-profit company general manager Carol Vosloo said: “We have developed a comprehensive action plan and are implementing a range of water-saving and alternative water-sourcing initiatives.”