Thanks to its famous coastline and peninsular setting, tourists in Cape Town expect that they will be surrounded by water — and lots of it. But as visitors have descended this month for the peak summer tourist season, they have been greeted at the airport with signs beseeching them to “Slow the flow: Save H2O” and “Don’t waste a drop!” among others.

Cape Town is in the throes of a severe drought because unseasonably dry winters have led to dangerously low dam levels. As of mid-December, the city’s dams were at about 33 percent capacity, according to the mayor’s office, and what officials have dubbed “Day Zero” is looming: that’s the date the dams will drop below 13.5 percent, taps will be turned off, and residents will have to line up at 200 checkpoints across the city to collect daily water allotments, with police and military deployed to monitor the situation. As of Dec. 18, based on current consumption and expected rainfall, Day Zero is projected to be April 29, 2018.

“The city of Cape Town could conceivably become the first major city in the world to run out of water, and that could happen in the next four months,” said Dr. Anthony Turton, a professor at the Centre for Environmental Management at the University of the Free State. “It’s not an impending crisis — we’re deep, deep, deep in crisis.”

As the city races to implement alternatives through recycling, boreholes and desalination by February, residents are restricted to 87 liters (23 gallons) of water per person per day. “We are all in this together and we can only save water while there is still water to be saved,” Zara Nicholson, the spokeswoman for Executive Mayor Patricia de Lille, said in an email. Residents are asked to meet that number by limiting showers to two minutes, turning off taps while brushing teeth, avoiding flushing toilets regularly (“If it’s yellow, let it mellow,” as one sign puts it) and using recycled water when they do, not watering gardens or topping off swimming pools, and using hand sanitizer instead of soap and water. But as the city struggles to hit a household consumption target of less than 500 million liters per day, anxiety continues to build.