Below our feet, sewers hold a world of microbial information. That’s what MIT researchers are mining through, thanks to a pair of sewage sampling robots named (rather appropriately) Mario and Luigi.

For the last year, researchers have been sending the two robots into the underbellies of Boston and Cambridge, Massachusetts to study how diseases can spread through city populations. The project is a three-year-long effort in urban epidemiology, as well as an attempt to learn more about the things people put into their bodies.

In July 2015, the team launched the robots as a part of Underworlds, a project of MIT’s Senseable City Lab and Alm Lab. The robots are hauled through manholes and fitted with GPS devices that tell the researchers where they are as they make their journeys. They spend an hour or two inside a sewer at a time, vacuuming up samples as they drift around.

The researchers are making sure the data from those samples is local and traceable. That way, scientists can study what a specific neighborhood or block’s health looks like, and even pinpoint what their diets look like.

Luigi is a slimmer, faster, and cheaper version of the Mario sewer bot. Courtesy MIT Underworlds

“We aimed to ensure that toilet water was no more than 10 minutes journey from its origin and our sample point,” Eric Alm, the project's chief investigator, tells Tech Insider in an email. That’s opposed to, say, sampling sewage at a treatment plant, where it’s much more difficult to determine where everything came from.

“We find that the sewage looks much closer to stool and urine samples collected directly from individuals,” Alm says.

From the samples, researchers can detect viruses, bacterial pathogens, and biochemical markers from drugs (both illegal and illegal).

The researchers hope they’ll be able to use the data to inform policymakers on public health issues, like potential disease outbreaks.

Though waterborne diseases are less prevalent now than they once were — typhoid and cholera both had devastating international pandemics in the 19th and 20th centuries — they still ravage cities with poor water sanitation. Typhoid fever is still prevalent in India; according to a study published in The Lancet, the disease affects 493.5 people out of every 100,000 annually — that's nearly 6.18 million cases in the country every year.

The researchers can also find out whether a certain part of the city has a drug problem, or measure the effects of food-related legislation, Professor Carlo Ratti, the project head, told Quartz. For instance, if a city imposes a tax or ban on certain foods (like New York's failed ban on large sugary drinks), the team could observe how people change their diets in response.

And while MIT’s researchers aren’t yet sending the robots into the world's most contaminated sewer systems, the data and findings they hope to submit to local lawmakers could serve as a justification for expanding the program to other cities. They're already planning to use the robots in Kuwait in 2017 as part of their partnership with the MIT-Kuwait Center for Natural Resources and the Environment.

“Funding will come directly from the stakeholders that benefit from the data: companies, governmental and non-governmental organizations,” Ratti tells Tech Insider.

As the saying goes, one man's trash is another man's treasure. Now we can say the same for sewage.