When they reach 13.5 per cent - a point the city is calling Day Zero, predicted to hit on April 16 - the authorities will turn off most of the city's taps, and residents will have to get their water at about 200 collection points monitored by police and the military.
Officials have acknowledged that the problem is almost unavoidable, potentially making Cape Town the first major city in modern times to run out of water.
The drought "is a catastrophe" said Neil Armitage, head of the University of Cape Town's urban water management department. "It's like waking up one day to a magnitude 7 earthquake. Everyone is in a panic."
Capetonians are stockpiling water, clearing supermarket shelves of plastic bottles. Police stand guard at natural springs after fights broke out between people queuing, and the city's tourism industry is suffering as sun-seeking visitors stay away.
Though the city is scrambling to get more water using groundwater and desalination plants, many frustrated residents accuse the city of mismanaging the water supply.
"They've had years to plan for this," said Bill Kennedy, wiping sweat from his brow after hauling 20 litres of spring water to his car in the midday sun. He said he was thinking about leaving the city before April 16. "Can you imagine when D-Day comes?"
As of this week, residents are only permitted to use 50 litres of city water each per day - about enough to drink, wash a sink of dishes, take a two-minute shower and flush the toilet once, according to city data.
Whether they meet that target, and potentially avoid Day Zero, remains to be seen. Only 55 per cent of city residents were meeting the previous 87-litre requirement.
At home, Capetonians have been forced to get creative. Baths are out. Hand sanitiser is in. Residents take brief showers over buckets every few days, and use the water to flush their toilets. Sales for products such as dry shampoo and wet wipes are up, and tanks for collecting rainwater are increasingly hard to come by.
A black market for water has predictably sprung up, and legitimate businesses are also experiencing a boom as desperate residents seek new ways to survive.
In the Stonehurst Mountain Estate, an upmarket housing development, Trevor Hennings has installed more than a dozen boreholes that tap into the aquifer beneath the city for residents who want to go off the grid at the hefty price of up to 250,000 rand ($28,000).
"There's blind panic now," said Hennings, owner of Drillco. In a normal year, Hennings says he has 10 or 20 clients on his waiting list for boreholes. Now he has about 6700.
"I've done whole suburbs. I've drilled Cape Town like Swiss cheese."
But for people who make a living off tourism, the water crisis poses a serious threat. Cape Town attracts millions of visitors a year, and tourism accounts for more than 7 per cent of the city's gross domestic product and tens of thousands of jobs.
"From a guest-experience perspective, not being able to flush a lavatory is a disaster," said Alison McKie, group commercial manager for the Petousis Hotel Group.
