Her announcement followed a directive by the DA federal executive that the Cape Town caucus must propose and pass a motion barring De Lille from being involved in the city's drought response.
The city has rolled out a string of projects in recent months to increase its water reserves, including efforts to drill into aquifers and the construction of desalination plants. The study ran from 2003 to 2013 and found that in 21 of the world's largest aquifers, more water was removed than replaced during the decade.
Nearly 2 million tourists flock to Cape Town every year to bathe on sandy white beaches, explore natural features like Table Mountain or to sip wine in dozens of nearby vineyards.
A top city official implicated in alleged tender irregularities was placed on precautionary suspension by the Cape Town city council on Friday.
"It has nothing to do with the proposal before us", ANC councillor Xolani Sotashe said. As we speak now, Capetonians have decreased their water usage to 587 million litres per day, so the messages work to drive down demand'.
The drought-stricken city announced on Thursday that it will begin marking 200 collection points where its 3.7 million residents will be required to queue for a rationed supply of water on "Day Zero" - now forecast to be April 21.
Mayor De Lille said the city would unveil 200 water collection points across the city next week "so that communities can begin preparing for that eventuality".More news: Blue Jays acquire OF Randal Grichuk from Cardinals
Cape Town has been caught in the throes of an unprecedented drought for three years.
More than four million Cape Town residents have also been instructed to shower rather than bathe and to keep it quick - under two minutes.
The researchers used the GRACE satellites to take precise measurements of the world's groundwater aquifers and detected subtle changes in the Earth's gravitational pull, noting where the heavier weight of water exerted a greater pull on the orbiting spacecraft.
"Everyone is taking as many steps and measures that they possibly can to try and make sure we don't reach Day Zero", said Gabrielle Bolton, spokeswoman for the five-star Belmond Mount Nelson hotel.
City officials say dam levels dipped below 30 percent in the first week of the new year, with only about 19.7 percent of that water considered usable.
Strong summer rains saw much of southern Africa recover from a drought induced by the El Nino weather phenomenon.