As Cape Town suffers its worst drought in a century, residents were warned this week that they face losing piped water to their homes on 12 April - nine days earlier than predicted.
If drastic consumption reductions are not achieved by "Day Zero", people will have to queue at 200 standpipes for daily rations of 25 litres.
The city, which attracts millions of tourists every year, has enforced strict waste controls, including prosecution of homeowners who use more than the current 50-litre daily limit.
A typical shower uses 15 litres per minute while a standard toilet consumes 15 litres per flush, according to WaterWise, a South African water usage awareness campaign.
"Due to a drop in the dam levels of 1.4%, Day Zero has, as of today, moved forward to 12 April," said deputy mayor Ian Neilson in a statement.
Every day that consumption exceeds 500 million litres, so-called "Day Zero" - the last day of normal water supply - draws closer.
"It is still possible to push back Day Zero if we all stand together now and change our current path," he said.
The previous forecast for "Day Zero" was 21 April.
That date was set on 16 January, bringing forward by one day a previous prediction of 22 April.
Earlier this year, the city published a name-and-shame list of the worst water offenders in Cape Town, and it says it is issuing fines for the heaviest water users.
But officials have been criticised for failing to implement usage restrictions sooner, and accused of ignoring warnings by experts in the years before the drought.
Strong summer rains saw much of southern Africa recover from a drought induced by the El Nino weather phenomenon.
But Cape Town receives most of its rain in the southern hemisphere's winter and scientists warn there is no guarantee of a good rainy season.