When was the last time you talked about toilets — really talked about them?

We all use them every day, but it doesn’t exactly make for good dinner conversation. We don’t like to think about what happens after we flush. Yet in a world wrestling with climate change, dwindling water resources, and aging infrastructure, one of the simplest, smartest, and most overlooked sustainability solutions is right under our noses — and we’re too squeamish to talk about it.

A standard toilet uses about 9 liters (2.4 gallons) of water per flush, but older toilets can use up to 13 liters (3.4 gallons). What if that’s not mandatory, and we could make do without the water? Do composting toilets, long relegated to off-grid cabins and eco-fantasies, deserve a seat at the table in mainstream urban planning, climate policy, and everyday life? At the very least, they should be considered. Here’s why.

Sanitation Makes the World Go Round

Modern sanitation is one of the most important (and underrated) inventions in our society. But in some ways, modern sanitation also works on a century-old model. Toilets connect to water lines for flushing and sewer pipes for waste disposal. It’s a system that works — but at a steep cost.

Water and wastewater treatment facilities consume about 3% of total U.S. electricity. And this is mostly to treat and move water that’s used, among other things, to flush human waste. According to researchers, 27% of indoor residential water use goes to toilet flushing. In schools, that figure rises to 60%.

It’s not just wasteful — it’s expensive. Leaks, overflows, and systemic inefficiencies are increasingly common, especially in older cities, with necessary repairs being on the order of tens if not hundreds of billions of dollars per year.

Chirjiv Anand and Defne Apul from the University of Toledo suggest that composting toilets could be an alternative, at least in some instances.

“Composting toilets require little to no water and can therefore disconnect the toilet from both the water supply and wastewater infrastructure. Such water and wastewater savings can be significant at system level since toilet flushing constitutes the highest percentage of water use in residential (27%), office (51%), school (60%), and hotel (33%) buildings,” the researchers note in a recent study.

“Another advantage of composting toilets is in nutrient cycling and transportation. Similar to solids obtained from traditional waste-
water treatment plant, the solids obtained from composting toilets can also be used as a fertilizer; yet they would be free from the ur-
ban runoff contamination and may require less transportation if they can be applied where compost is produced.”

A Surprisingly Long History

Composting toilets offer a different approach — decentralized, waterless, and nutrient-recycling. Instead of flushing waste away, they treat it on-site. Using aerobic composting, they break down organic matter into humus, carbon dioxide, and ammonia with the help of bacteria, fungi, and time.

In the process, they generate a byproduct that, when properly managed, can be used as fertilizer for non-edible plants or even as soil conditioner in urban landscapes. And they do it using little or no water, minimal energy, and no sewer connection.

In other words, they offload pressure from overburdened municipal systems while conserving water.

“Composting toilets offer good promise as a sustainable solution,” the authors write, noting that they align with ecological design principles — like decentralization, multi-functionality, and low energy input — that are gaining ground in modern urban planning.

The very first dry toilet was called the earth commode. It was made of wood and was invented in 1860 by Henry Moule. The flush mechanism of this toilet released soil into the commode every time the flush was used. The closet was shallow, allowing aerobic decomposition.

But since then, composting toilets have also come a long way.

What Compost Toilets Are Like Nowadays

By now, you’re probably imagining some old school toilets that probably smell. Anand and Apul say that’s not the case.

They documented a wide variety of designs — from self-contained units in single-family homes to central composting tanks connected to multiple toilets in multi-story buildings. Some require no electricity and function with passive aeration and manual mixing. Others use heating elements, fans, or even vacuum systems for enhanced efficiency and odor control.

There are single-chamber systems, where all waste composts together, and multi-chamber models that separate fresh and aging waste for better control. Some even employ carousel-style drums or bio-drum systems that automate the composting stages. The two scientists also identified the key factors that influence composting performance — such as moisture content, temperature, aeration, and carbon-to-nitrogen ratios. And they explored how different system designs address these needs.

When managed correctly, composting toilets are capable of producing a stable, pathogen-free material suitable for use as a soil amendment. The composting process — especially at high temperatures (55–65°C) — destroys harmful bacteria, viruses, and parasites. Time–temperature guidelines, such as maintaining 55°C for at least 3–15 days, are effective in killing pathogens like E. coli, Salmonella, and Listeria. Urine, when separated, is typically already low in pathogens and high in nutrients, making it even safer and easier to reuse.

Some systems also include additional finishing chambers or allow compost to cure over time, further reducing risk.

Can Composting Toilets Actually Be Scaled?

Composting toilets are viable in a wide range of settings — from rural cabins and tiny homes to urban apartments, public parks, schools, and even multi-story buildings. They use little to no water, don’t require connection to a sewer system, and can significantly reduce the burden on aging or overtaxed sanitation infrastructure. There are many models available — electric, non-electric, urine-diverting, multi-chambered — and users report high satisfaction when the system is installed and maintained correctly.

Despite the promise, composting toilets remain rare. The first problem is regulatory acceptance. Most building codes and sanitation laws are designed around flush systems. Composting toilets exist in a gray zone, and local codes vary widely. The lack of knowledge and social acceptance is also hampering their growth.

Still, the authors see growing momentum. Green building standards like LEED now award points for composting systems. More commercial models are hitting the market. And a new generation of climate-conscious homeowners and builders are asking questions that go beyond the flush. The technology is already proven, adaptable to different settings, and increasingly recognized in green building standards.

Composting toilets won’t replace flush toilets overnight. But they should be part of the conversation — especially as cities confront water shortages, infrastructure failures, and climate goals. At least in some instances, they could be useful.

These toilets conserve water. They reduce energy use. They produce something valuable. And they challenge us to rethink waste — not as something to get rid of, but as something we can reclaim.

As Anand and Apul conclude, “It is timely to revisit the status of composting toilets and bring awareness to this technology so they can be better evaluated for possible adoption.”