Day zero can be expected as soon as April 29, 2018, after high water usage by Cape Town residents over the past week, the City of Cape Town said on Tuesday.
According to the City, day zero is when almost all of the taps in the city will be turned off and residents would have to queue for water at approximately 200 sites across the peninsula.
Some essential services would stay connected, but almost all residential suburbs would be cut off.
The City said in a statement that total water storage had decreased by 1.1%.
Dam levels were standing at 33%, while the city's overall water usage had risen to 641 million litres per day.
Only 34% of residents were saving water and agricultural users had consumed water at a similar rate to the city, the City said.
Director of Water and Sanitation Peter Flower described it as a "terrifying prospect".
"If water consumption continues to rise, together with the very hot windy conditions which increase evaporation losses, we can expect day zero to happen [sooner]."
Flower said residential customers remained the largest portion of water users.
He added that, if residents brought consumption down to 500 million litres per day, day zero could be avoided.
Teams were hard at work to ensure that the average response time to leaks or burst pipes would be under two hours, he said.
Flight bookings up 7%
An additional 40 000 water management devices from would be enrolled to high consumption households that ignored water restrictions from January onwards.
The City has installed more than 21 000 water management devices on the properties of high users to date. This is expected to continue through December.
Level 6 water restrictions were expected to come into effect from January 1, 2018.
Households who use more than 10,5 kilolitres per month, would have a water management device fitted.
Chief Marketing Officer at Wesgro, the official tourism, trade & investment promotion agency for Cape Town and the Western Cape, Judy Lain said the number of tourists travelling to Cape Town for the festive season could not be confirmed yet.
Lain said domestic tourists were increasingly making last-minute bookings, which made them difficult to track.
Lain said between January and March 2017, the Western Cape had attracted a total of 1 000 156 international and domestic visitors.
"Of these 472 156 were foreign tourist arrivals, a six percent increase from the same period last year. If this rate is replicated, we should see a similar increase over the summer peak season."
Between October and December 2016, there were approximately 450 000 foreign tourists in the Western Cape.
According to Forward Keys Bookings, flight bookings for Cape Town for December 2017 was up seven percent compared to December 2016.