Visitors to the Finnish pavilion at 2023’s Venice Architecture Biennale are greeted with an unlikely sight at a festival typically devoted to the avant-garde and newfangled: a no-flush outhouse toilet.
While the structure, known as a Huussi, may seem a bit primitive to some, it’s long been a popular toilet design in rural parts of Finland because it requires no connection to water supplies: It processes waste not by flushing it away, but by converting it to compost in a hay-filled container. It’s a design that’s making a comeback because it saves water and recirculates waste back into the ecosystem — both essential goals in a world where many areas are drying out thanks to climate change, and where as much as 30% of urban water supplies are used to flush human waste. Our modern toilet practices are likely to become unsustainable within the next few decades; by 2050 it’s estimated that up to five billion people could be facing water shortages.
Toilet composting could also fuel an alternative to the carbon-heavy manufactured nitrogen fertilizer and mined phosphorus widely used in farming today. Chemical fertilizers also deplete carbon from one of the few places we want to retain it — in the soil itself, where it fosters vital microbial activity.
Some designers in Finland are looking to the recent past for more sustainable, hygienic solutions for sewage, while others are using more modern technologies to reduce or eliminate the need for water. Part of what the exhibit at the Venice Biennale, open until Nov. 26, highlights is that these toilet designs are far less offensive to our modern olfactory sensibilities than many might assume. Here are some of the ways that architects and planners are rethinking toilet systems to help them fit into a circular economy, reducing the excess water and pollutants that billions of us literally flush down the toilet.
The Modern-Day Outhouse
The central attraction in the Finnish Pavilion, the Huussi latrine shack, will likely be recognizable to local visitors. It’s a type of outhouse once common in the countryside and still a regular feature in many of the country’s summer cottages. Located outside the house, a Huussi has no running water but instead voids its waste into a hay, wood chip or sawdust-filled compartment, over which each user shovels a layer of extra wood chips after use. While the traditional Huussi toilet was sometimes little more than a malodorous bucket, modern versions do not smell: The dry contents of the composting compartment neutralize this, while any urine that can’t be absorbed is siphoned off into a separate biofilter — typically a plant-filled container where the nitrate-rich liquid is filtered through (stench-free) layers of gravelly soil.
The outhouses’ familiarity, and their association less with a past of poverty than with appealing rural escape, make Finns less squeamish about this system, which is now leaving the countryside and heading back to Helsinki — albeit to the city’s greener fringes, where dry Huussi-style toilets are being installed in places where sewer connections are lacking or limited. In the Finnish capital’s forest-fringed, island-speckled location, such sites are surprisingly common.
“In Helsinki we have recreational areas that aren’t simply parks but a combination of parks, forests and nature reserves,” said Helsinki Chief Design Officer Hanna Harris. “I’m sitting in downtown now and there’s a nature conservation area less than a kilometer away. So the areas where we are trialling outhouses aren’t dense housing areas; they’re natural ones where the project’s down-to-earthness has really captured people’s imagination.”
Such facilities make perfect sense in Finland, with its relative spaciousness, cool climate and cultural familiarity with the concept. They also, to an extent, make sense in Venice’s scattered, sewer-less lagoon — once the biennale ends, the Finnish outhouse will be relocated to the lightly populated outlying Venetian island of Vignole, whose fields are also a suitable destination for any fertilizer produced.
And elsewhere in the developing world, toilets that compost can be particularly beneficial: Manufactured fertilizers — aside from being polluting — are becoming increasingly unaffordable for farmers, leading to lower yields and higher food prices in the places where populations are most likely to be affected by them.
Airplane-Style Vacuum Toilets
Even well-designed and odor-free, a Huussi-style model might seem off-putting to many. But the system the exhibit advocates for widespread contemporary use in urban areas is something very different: sustainable medium-scale vacuum toilets along the lines already used in aircraft.
Facilities like these require a fraction of the water of a conventional toilet and are scalable to systems capable of serving up to 2,000 units. They require a small amount of electric power to function and use as little as half a liter (just over one pint) of water to flush, as opposed to up to 10 liters for a regular toilet. Even this half liter is used twice, as its cistern is filled with water channeled from a sink after being used for handwashing.
These facilities not only save water but also fuel a circular economic system. Rather than hitting the sewers, their waste can be channeled to district-level cesspools where they can be converted into nutrient-rich fertilizer by anaerobic digestion. The methane produced by this process can also be siphoned off to use as fuel, possibly for the district heating systems that, while not ubiquitous, are common in Finland. Given that much of the fuel for these district heating systems is still highly polluting coal, even this byproduct could help reduce Finland’s carbon footprint.
The Future of Sewer Alternatives
Finland is not the only country in the biennale thinking about less-wasteful toilets. As part of an exhibit exploring wider issues of reuse, Germany’s pavilion also displays a water-free toilet — one that, unlike Finland’s Huussi, is actually useable in its current site. The approach is slightly different on another level — rather than removing excess urine from a shared tank, it separates liquid and solid waste to two different tanks in the bowl itself.
Beyond the biennale, ways of making toilets more sustainable have been taxing experts for some time. The Bill and Melinda Gates Foundation has been running a Reinvent the Toilet Challenge since 2012. Models developed since then have included toilets that burn waste and can filter water to drinking quality, providing heat and power as they do so. International standards for non-sewered toilets have also been devised as guidelines. Provided that systems like these are kept in working order and contain no leaks, there are no inherent environmental downsides to their use. The problem, however, is that their installation can be expensive. If larger sewage processing systems were broken down into smaller ones, the process of collecting and reusing waste could also be notably more costly and complex. Reducing pressure on systems like these through more local composting could ease pressure on sewers barely improved or enlarged since the Victorian era.
Despite the potential advantages of dry or greywater toilets, they remain rare on a large scale. Their effectiveness has nonetheless been demonstrated by a few pilot projects. In the Dutch town of Sneek, a project serving 232 homes and an office building has worked with a vacuum toilet system since 2010. In its first year of operation, the project’s overseers found that the system enabled homes to cut their water use by 50% and their heating fuel use by 10%, because the process of converting the microdistrict’s waste to fertilizer produces biogas as a byproduct, which is then used for in-district heating.
But such projects remain unusual outliers. The barriers to their broader uptake are similar to those facing many climate-adaptive innovations: To replace a sewer system that — despite heavy water use — functions well enough and is expected as a standard feature by building occupants, risks being complex, expensive and subject to tenant resistance. Installing a network of vacuum toilets and cesspools for anaerobic digestion could be a major undertaking in a world where such facilities remain rare and — without mass production — expensive.
Dry or minimum water systems are thus more likely to flourish initially in places with no or limited sanitation — in new developments, for example, or parts of the developing world where insufficient investment has forced people to use impromptu, imperfect solutions.
A city served by several smaller-scale utility systems is also more likely to stay resilient in a future ever more greatly affected by climate change. Rising sea levels and extreme weather are already making a lot of essential infrastructure more vulnerable to breakdown, and the larger the system, the greater the number of people likely to be impacted by an outage.
And as people increasingly start to move en masse to less vulnerable locations, systems like these tend to have components that are easier to dismantle and reassemble, making them suited to an urban future where adaptation, mobility and maybe even nomadism will become key shapers of the city.
The Finnish pavilion’s curators acknowledge that we are just at the beginning of making sustainable toilet systems mainstream. That in itself, they emphasize, needn’t be a deterrent.
“Certainly it could be up to 50 years before this kind of system has spread across the world,” said curator Arja Renell. “But we have to start somewhere.”
Feargus O’Sullivan is a writer for CityLab in London, focused on European infrastructure, design and urban governance.