She does not believe people will comply, and Day Zero will be around April 12.
Local authorities have warned four million people that if they do not reduce consumption by "day zero" - 12 April - they will have to queue at 200 standpipes for daily rations of 25 litres (6.6 U.S. gallons).
On Monday, Zille said that she had written to President Jacob Zuma, asking for a national disaster to be declared after the likelihood of Day Zero was confirmed by the City of Cape Town. A single flush of a toilet uses around 15 litres.
Residents are only permitted to use 50 litres of water per day right now, but not all Capetonians are listening to those rules.
"It is still possible to push back day zero if we all stand together now and change our current path".
Residents of Cape Town, one of the world's most popular tourist destinations, could be forced to queue for emergency water by April as the city battles its worst drought for a century.
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Shiao also expects an 11 percent reduction in solar installations over the next five years because of the tariffs. Supporters of trade barriers say they will protect domestic industries from harmful overseas competition.
However, the measures have not been enough, forcing local officials to bring forward "day zero" by nine days.
South African Tourism CEO Sisa Ntshona added: "We are pleased that we have not received any reports of any tourism attractions and services interrupted by the water shortage and we appeal to tourists, and tourism businesses to continue being good responsible tourism citizens and continue being water-wise, even as the peak holiday season in South Africa winds down".
A statement from Michael Mpofu‚ spokesperson for premier Helen Zille‚ said managing the crisis meant the bulk water supply would have to be increased‚ and the provincial and city government were doing this.
Cape Town is the second-most populous city in South Africa.
"As a department we have successfully intervened and saved several provinces who were devastated by the drought over the last three years and will continue to do so in the Western Cape as well".
A long drought as well as a booming population and poor city planning have exacerbated the situation.