Thomas Crapper, the brains behind the modern flush toilet, likely had no idea there would be over seven billion people living on this planet. The materials, energy and dollars spent on infrastructure and operation of using perfectly good drinking water to flush away our "poop and pee" away is considerable and growing.
Back in the days of the "night cart", it was commercially sustainable to harvest, process and use the nutrients from human waste, but when mixed with water both commodities become useless. However the "water closet" became fashionable and a status symbol, and its future was assured.
The current drive to conserve water, or even achieve net zero water and to re-learn how nature processes waste, has resulted in a range of innovative solutions; from hand basins feeding toilet cisterns; to small local plants using reed beds to recycle water for flushing; to compost systems and onto nutrient recovering algae farms. The technology and options are evolving fast.
Composting toilets have the lowest lifecycle impacts of all options - they eliminate water and infrastructure. Unfortunately we all know about the ones that fail and pong.
Modern composters are well vented, drawing air through the chamber to remove smells and dry out matter. Many use separators to keep the liquid pee out of the mix, saving the nutrients for use on farms, fruit trees and shrubs. The output from a good composter should look no different to your bag of potting compost.
Composters do need to be designed into houses as they often have a lower-level chamber, or a more energy hungry drying model will need to be used. If we want state-of-the-art, sustainable or even "living" houses and buildings, especially on small urban sites, the modern composting toilet will likely be part of the solution.
A recent six story office building in Seattle, the Bullit Centre, has super low-flush foam toilets with basement compost units, to eliminate 70 per cent of water use.
Read more about composting toilets at sustainable building website Level.