São Paulo residents block a road in protest of water cuts. Nacho Doce/Reuters

Here's a scenario that seems plausible enough: The Brazilian megacity of São Paulo, currently dealing with Brazil's largest water crisis in 40 years, continues to experience severe drought over the next several months.

The crisis deepens, and soon, some residents lose access to water altogether. The next step: a riot or crowd-driven attack on Sabesp, the local water utility.

It's the kind of desperate measure that seems more like a distant post-apocalyptic situation for other drought-ridden places like California, but as one São Paulo water activist recently discovered, the Brazilian army is actually preparing for this possibility.

"I looked at the emergency plan from the government. They don’t know how we’ll save water," explains Martha Lu, a water activist, in an interview with Tech Insider. "The army is in Sabesp doing an exercise to prepare for an invasion from the people."

This past May, Lu teamed up with a journalist from Spanish newspaper El País to visit Sabesp while the army was involved in one of its riot simulations. You can read their full report (in Portuguese) here.

Sabesp told Lu and journalist Maria Martin that the army has been doing similar exercises for 15 years, but former employees of the water utility contradicted that, saying that they had never seen anything like it.

Pontoons in the dried-up Atibainha dam. In wetter times, they float. Paulo Whitaker/Reuters

On the day that Lu visited Sabesp, approximately 70 army members were scoping out the utility's readiness for an uprising. One official said that 30 men with machine guns were stationed in the lunchroom.

São Paulo has also reportedly sent public officials to the US to take lessons from SWAT leaders on how to deal with the water crisis.

Already, people in the city are experiencing water cuts that last from hours to days at a time. Prior to the drought, the city's water supply provided 8,700 gallons of water each second. That's now down to 3,563 gallons per second. As a World Bank official told NBC News, "São Paulo's current drought emergency is both unprecedented and unpredicted."

The rest of the world should take note: the way that São Paulo residents and officials react if the drought continues will be a preview of how things will go elsewhere — in California (and other parts of the U.S.), China, India, France, and every other place where that the water table is dropping— without drastic water conservation measures.