Design for Living: When water is too precious to waste

Finnish dry compostable toilet on show at the Venice Architecture Biennale.

What would we do if the world started running out of fresh water? Oh no, wait, it’s already happening. One thing we’re going to do – not all of us everywhere but far more of us than you might think – is stop flushing. Water will be far too precious to waste on waste, so dry compostable toilets will probably become common.

Finland has the concept on display right now at the Venice Architecture Biennale. The toilet is in an outhouse and no water is involved. They call it a huussi.

Huussis aren’t new, Finns have long been using them in parts of the country where water connections are hard to establish. You do your business sitting on a normal toilet seat and the waste falls into a container of hay, wood chips or sawdust. When you’ve finished, you trowel a covering layer of wood chips into the container.

Just another Finnish Huussi.

Smells are neutralised by the dry contents and, if there’s more urine than can be absorbed, it’s filtered through another container containing plants and gravelly soil. That doesn’t smell, either.

By 2050, at current rates, it’s estimated half the world’s population won’t have enough water. Yet in some parts of the world 30 per cent of the available water is flushed down the toilet.

Dry composting toilets put an end to that, and it’s not the only benefit. The system provides an alternative to manufactured nitrogen fertiliser and mined phosphorus, both of which are commonly used in agriculture. These chemical fertilisers not only produce carbon emissions, they take that carbon from the soil, which reduces the valuable microbial activity.

In the developing world, manufactured fertilisers are also becoming more expensive, which makes them less affordable and leads to lower yields and higher food prices.

Dry composting toilets aren’t the only alternative to flushing, especially in cities where it isn’t practical to build tens of thousands of outhouses. Fancy an aeroplane-style suction toilet in your house?

They use a little bit of electricity and only half a litre of water, and even that is used twice, because the water you wash your hands in gets routed to the cistern. As for the waste, if your sewage system is past its use-by, it can be piped to local cesspools and converted anaerobically into nutrient-rich fertiliser. And suction toilets can be scaled up for everyone. Woosh.

What about toilets that burn their waste, providing heat, and filter the water to drinking quality? They exist, thanks to the Reinvent the Toilet Challenge started by the Bill and Melinda Gates Foundation in 2012. Currently, they’re expensive to install, but these things change.

There are other problems, not least being that everyone building, consenting, buying or renting a home expects there will be ordinary toilets in it. But it’s early days. The Dutch town of Sneek has had a vacuum toilet system operating since 2010. In parts of this country that have to get serious about managed retreat, some councils and homeowners may decide the alternatives to ordinary are quite appealing.

In New Zealand, several companies sell dry composting toilets. You can even try before you buy: the Whangārei District Council has recently installed some at Matapouri Beach.

You can make your outhouse as friendly as you like.

Design for Living appears most weeks in Canvas magazine.