As Cape Town suffers its worst drought in a century, residents were warned by the mayor on Tuesday that they face losing piped water to their homes by April 21.

If rains do not materialise and drastic consumption reductions are not achieved by "Day Zero", the city's people face the prospect of queueing at standpipes for daily rations of 25 litres (9.2 US gallons) of water.

The city, which attracts millions of tourists every year, has enforced strict waste controls including splash bans at municipal pools and hauling homeowners using more than a 87-litre daily limit before the courts.

In the past week, just 39 percent of Capetonians used less than that amount.

"Cape Town's average daily collective consumption is still too high. It has increased to 618 million litres per day` up from 578 million litres per day (since the first week of January)`" said mayor Patricia de Lille.

Every day that consumption exceeds 500 million litres, so-called "Day Zero" -- the last day of normal water supply -- draws closer.

"Dam levels have dipped to 28.7 percent this past week," she told local media as she announced that "Day Zero" would happen one day earlier than previously forecast. It was previously predicted for April 22.

"The city has ramped-up pressure management to drive down consumption -- aiming to stretch our water supply past the winter rainy season."

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 themselves have faced criticism for failing to implement usage restrictions sooner, and have been accused of ignoring warnings by experts in the years before the drought.

City workers are now seeking to use groundwater from three local aquifers, recycle waste water and step up production at three desalination plants.

Some Capetonians have taken to collecting their own water at a natural spring outside a brewery in the city.

Many are convinced that with dam levels so low, the quality of tap water has declined -- a rumour that the city has been battling for months.

Strong summer rains saw much of southern Africa recover from a drought induced by the El Nino weather phenomenon.

But Mediterranean-like 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.