Compost toilets don’t feature in bathroom catalogues and yet they are one of the iconic green building technologies.

So it is worrying that a recent Guardian Environment Network article reported on the failure of the “world’s biggest eco-toilet scheme”. Residents of the Daxing eco-community in Inner Mongolia suffered serious odour and health problems before winning a battle to have conventional flush toilets installed.

The residents are now happier but the article suggests that the community has “lost its most important symbol” the dry toilet. The flush toilet and piped sanitation is arguably the most important symbol of modern civilisation. If waterless toilets are the most important symbol of a sustainable alternative then in the light of this story we need to revisit the technology and/or our thinking about what is sustainable.

When we built our home my partner insisted on a dry toilet not for green reasons but for functional and aesthetic reasons. After many years of research and tinkering we knew how to make a compost toilet that had absolutely no smell, was silent in use, needed no water and was easy to clean.

By comparison a flush toilet is smelly, splashy and noisy and, in our rural location, usually requires an annual visit from a sludge tanker to empty the septic tank. We love our compost loo and yet I regularly talk enthusiasts out of them. This is because of a number of mundane considerations such as the need to design the building around the toilet and the fact that a compost loo is living thing that will fail if abused or neglected. For all its shortcomings, the flush toilet does a good job in a wide range of situations and with good design it need not use much water either.

Conversely, I have heard advocates of less effective dry loos argue that it is morally wrong to flush and forget, that it is right to be reminded that our shit smells. I’m not of that school of thought. I strongly believe that “sustainable” technologies have to work better than conventional ones, for me that’s part of the definition. An eco-car will never go as fast as a Maserati but few choose to drive a Maserati and it’s not just a question of insufficient wealth.

[locate Architects.jpg A Natsol dry toilet with building designed by Chris Morgan, Image courtesy of Locate Architects http://www.locatearchitects.co.uk/salen.htm]

Don’t confuse my scepticism with cynicism as I rubbish yet another green icon, it is only the unquestioned iconic status that I wish to rubbish. In 2005, I set up a small company with long time collaborator Andy Warren [www.natsol.co.uk]. We wanted to develop a state of the art compost loo for applications such as allotments and remote sites where we thought they really made sense. We now have over 300 installations and the business is going from strength to strength. This is because the product aims to be a “better mousetrap” not because we have identified a naïve consumer group eager to buy into a green lifestyle.

Uncommon sense

It does feel wrong to shit in pure drinking water but as often happens in this field, when we take a dispassionate view, the self-evidently wrong approach can turn out to be the most environmentally and socially responsible. Mains water has a lower life cycle impact than rain or grey water in the UK and gravity sewers are a zero energy miracle of Victorian engineering that have required surprisingly little technological improvement.

However, I had always assumed that dry toilets would be the technology of choice for low cost sanitation in slums where the water supply is at best erratic. It doesn’t take much imagination to appreciate the benefit of a simple hole in the ground over a heavily used Western style toilet without a functioning water supply. But an inspiring RSA lecture by Himanshu Parikh in 2004 turned my assumptions on their head in the way the best talks and writing do (Ted version of the talk). Parikh’s story of the far reaching and cost effective transformation achieved by bringing low cost piped sanitation to slums in India is an excellent example of the application of science, uncommon sense, good engineering and the questioning of assumptions. Do watch the talk, the contrast with the Daxing story is profound.