The interaction of diverse people all packed inside a city can quickly lead to dynamic new ideas and inventions. Cities helps to foster communication, collaboration, and the exchange of ideas.

But when cities lack sufficient sewage systems, those same urban conditions can also lead to an exchange of bacteria and disease.

That’s where Sanergy comes in.

The organization gives communities in Nairobi, Kenya and other fast-growing cities the vocabulary to discuss defecation and the tools to manage human waste.

“A city is a system of networks connecting residents to services and to each other,” said Sanergy operations manager Lindsay Stradley in a TED Talk published Thursday. “But what happens when one of these networks is missing?”

Take Action: Urge Governments and Businesses to Invest in Clean Water and Toilets

When a sewer system is missing, it means that residents frequently encounter — or even drink — water contaminated by human feces. That dirty water causes deadly diseases like typhoid and cholera. Such illnesses spread rapidly through densely populated areas with insufficient sewer systems, including the parts of Nairobi where Stradley works.

“In the informal settlements, Nairobi reminds me of post-Katrina New Orleans. Residents are disconnected from networks and services,” Stradley said. “For cities to thrive, we need to talk about how to build smarter systems that service the cities of tomorrow.”

To solve sanitation problems in cities like Nairobi, where the population has doubled over the past 30 years, Sanergy employs local workers who distribute high-quality toilets, collect the waste, and repurpose it for various uses. For example, Sanergy provides fertilizer for farmers in the region, Stradley said.

But, despite being a huge public health concern, residents are often conditioned not to discuss poop.

Read More: 5 Ways You’re Wasting Water Without Even Knowing It

During her TED Talk, Stradley described how taboos around defecation — especially for women and girls — discourage frank conversations.

“Lindsay Stradley brings up an important sanitation issue that spans the world: No one wants to talk about poop,” TED writes. “So, human waste becomes an unresolved issue in many developing regions.”

Like Sanergy, Global Citizen campaigns on ensuring all people, no matter where they live, have access to safe sanitation systems. You can take action here.

According to the World Health Organization, 2.4 billion people around the world are cut off from appropriate sanitation systems. And children, who make up a huge segment of the population in Nairobi and other rapidly expanding cities, are most vulnerable to illnesses from feces-contaminated water, Sanergy co-founded David Auerbach told Global Citizen.

“Sanitation has a huge impact on kids,” Auerbach told Global Citizen. “In fact, kids are the ones who are the most at risk and most vulnerable to sanitation diseases, because their immune systems haven’t been fully developed yet.”

“Changing the status quo is extremely difficult,” Auerbach said. “Even if you have a great idea, it’s going to require just a ton of time, energy, grit, optimism and determination.”