At a Glance

Cape Town, home to more than 4 million, is in the midst of the worst drought to hit South Africa in more than 100 years.City officials say they will "turn off the tap" in April when dam levels are expected to reach 13.5 percent of capacity.

Officials in Cape Town have set April 22 as "Day Zero", the day the city will cut off water to residents unless drastic measures are taken to decrease usage.

The city that is home to 4 million is in the midst of the worst drought to hit South Africa in more than 100 years and is rapidly running out of water. The city said Tuesday on Facebook thatit will "turn off the tap" when dam reserves reach 13.5 percent. The date at which dam reserves are expected to reach that milestone keeps getting pushed forward.

The situation is dire. Dams supplying the city with usable water dropped this week to 29.7 percent, thecity of Cape Town posted to Facebook on Wednesday. Only 19.7 percent of the water is usable. Several times a day, the city encourages residents via social media to conserve water.

The South African city is a tourist mecca, and touristsare being reminded of the gravity of the situation when they arrive, thereports.

"A single flush uses 5 days of drinking water," a sign greets tourists. "Our tapswillrun dry if we don't act now."

To avoid Day Zero, the city has reduced water pressure and banned residents from watering gardens and washing cars. Most public swimming pools are closed, and the city resorted in February to shaming the top 100 water consumers by releasing their identities to the public.

In July, Executive Mayor Patricia de Lille to no more than 23 gallons a day, which is roughly equivalent to the amount of in a newer model washing machine, according to the United States Geological Survey. A single toilet flush can use up to three gallons of water.

On Monday, De Lille released a statement noting that to keep consumption under 23 gallons per day.

"This compares well to only 37 percent of Cape Town’s residents saving water during the first weeks of December 2017," she added. "But consumption remains too high with half of Cape Town’s residents still not keeping to the consumption limit of 87 liters of water per person per day."

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De Lille says she hopesit won't come down to Day Zero, but the city is already planning for that eventuality. Should the city be forced to turn off the taps, will be set up to rationout roughly 6.6 gallons (25 liters) of water per day per resident.

Cape Town isn't the only city dealing with water issues in a warming world.

The World Wildlife Fund estimatesmay face water shortages by 2025 as droughts become more frequent because of global warming.