Officials in the coastal city of Cape Town, South Africa recently designated July 9, 2018 as "Day Zero" – the day the city's water will run out.

More accurately, July 9 is the day reservoirs will reach a critical number, 13.5 percent of capacity, a point past which the remaining water is contaminated and not worth pumping. When this level is reached, officials will order engineers to turn off all the pipes in the city.

Mired in a 3-year drought, the severity of which is said to occur once every 384 years, Cape Town will almost inevitably become the first major city in the world to run out of water.

After the water mains are off, 200 water taps, under watch by security guards, will open around the city, where people will wait in line to get their allotted daily 25 liters of water. For perspective, the average American shower uses 65 liters. This is in a city where residents already use scant water, where unwashed hair has become a "symbol of upright citizenship."

However, Cape Town is only the beginning. According to Kelly Sanders, assistant professor in USC's Department of Civil and Environmental Engineering, water will be the defining crisis of the century.

"The tricky thing about water is you really can't solve the problem in a day or week or month, so you really have to start thinking about these problems decades in advance," Sanders said. "No one really cares about water until it's a crisis."

Sanders, who studies the "energy-water nexus," is an expert on human energy production and water consumption, and how to communicate to solve issues, like Cape Town, before they become unsolvable.

According to Sanders, resource scarcity is behind many larger geopolitical issues. She points to the current war and refugee crisis in Syria as an example.

"What caused the refugee crisis in Syria?" Sanders said. "Most people would say an unstable regime, but what underpins Syria is access to groundwater. Farmers lost cheap access to groundwater when subsidies were taken away. They couldn't afford water so they moved to cities. There were no economic opportunities in the cities so people were out of luck and had to leave."

Water scarcity in Los Angeles
In the coming decades, water shortages will have an impact on Americans as well. As climate change raises the average temperature of the globe, the water cycle will inevitably be impacted. Sanders emphasizes the impact the changing hydrological cycle will have on humans.

"I like to think of the ocean as a teapot," Sanders said. "As you add more and more heat you get more and more energy buildup and eventually you get steam. That's why you see things like much more extreme hurricanes this year."

This past summer included storms such as Harvey, Maria, and Irma, which caused a record amount of damage. In addition to more intense storms, the changing climate will also alter the distribution of water, which will increase the number of extreme droughts.

This includes California, which appears to be heading back into drought conditions.

Jill Sohm, assistant professor in USC's Department of Environmental Studies, is an expert on local water issues. Sohm notes the similarities between Cape Town and Los Angeles.

"One useful thing to point out is that Cape Town has the same climate as California — Mediterranean, with wet winters and completely dry summers," Sohm said. "That means you rely on the rains that happen in the wintertime and the storage of that water to get through dry period."

In the early days of Los Angeles history, city pioneer William Mulholland orchestrated the construction of the California Aqueduct, which brings water from Owens Valley to much of Southern California.

This detail is important to know when considering California's climate, and what Los Angeles relies on to survive. Because the state only gets rain during the winter, all of that water must be stored somewhere – the Sierra Nevada snowpack. Unfortunately, due to climate change and drought, the snowpack is far below average.

"Los Angeles wouldn't exist the way it does if we didn't have water coming in from other places," Sohm said. "Los Angeles has a lot of outside sources of water, but that also means we're vulnerable to things outside our city that are out of our control. There's pretty good evidence that the snowpack is going to be reduced in the future. If there's not as much rain or precipitation falling as snow, they will have less water to send down to Southern California."

The Future of Water Management
According to Sanders, Cape Town should serve as a warning to other cities to take action.

"At the very least, we have to agree that there's a problem and we have to accept that it's going to cost money, Sanders said. "One of the reasons why it's hard to be optimistic is that humans are reactive, not proactive. We like to react to crises as they happen."

Sanders believes that in order for these problems to be solved before they become so serious, there needs to be more integrated planning, which will lead to necessary communication between groups who are unaware of the way their actions influence each other.

"People in the energy industry need to be thinking about water," Sanders said. "Historically you throw up a power plant wherever you want to, and you don't think about whether there's enough water to safely cool this thing forever. On the water side, you need to think of the energy and ecological consequences of desalination."

In California, many options exist for lessening the state's water consumption and planning for potential water crises in the future. One such option involves new agriculture technology.

Jason Sanders, husband of Kelly Sanders, is national programs manager at EcoSafe Zero Waste, a company devoted to creating and implementing strategies for better organic waste management. He believes that advances in agriculture, which currently takes up 80 percent of California's water supply, will significantly reduce water demand in the future.

For example, one model of farming, called vertical aquaponics, can reduce water use by 90 percent. Jason notes that to have a major impact, innovations like vertical aquaponics require successful collaboration.

"When the [aquaponics] infrastructure becomes available on a mass scale that's when we're going to see a big water shift with annual crops like lettuces and leafy greens," Jason said. "Ideally it'll be public-private partnerships that'll go into join contracts to help build these systems."

Areas like San Diego County are also leading the way in forward-thinking planning. San Diego recently installed a series of reservoirs and pumps designed to hold its residents over if water from the north gets cut off. In 2015, the city of Carlsbad opened the largest desalination plant in the western hemisphere, though desalinated water still costs twice that of imported water.

On an individual scale, Sohm points out that people have been willing to make a difference as well. She brings up the fact that during the drought, Los Angeles was successful in getting its residents to achieve a 20 percent reduction in water consumption.

"As an individual, it's important to focus on the fact that you can do things differently," Sohm said. "You can try to encourage people around you to do things differently. And that does have an impact."

"Another thing the city of Los Angeles is trying to do is capture stormwater and store it so we have more locally sourced water. But infrastructure projects are long-term builds, so you have to be thinking out ahead."

According to Sanders, thinking ahead is important if cities like Los Angeles want to solve water crises before they begin.

"No one's ready to pay for water until it's a crisis," Sanders said. "Some communities will have to carry the burden to wake everyone else up."