One of the marvels of the modern city is its ability to make waste disappear. Along with electricity, water, and the internet, sophisticated waste networks allow residents to discard or flush away any signs of urban consumption. But this may be changing. As cities increasingly face the prospect of droughts and uncertainty about future water availability due to climate change, a new source of water is now being explored that might prompt city residents to pay close attention to its origin and fate: their toilets.
Wastewater reuse – known as “reclaimed water” to proponents, and “toilet to tap” to critics – is used to augment supply in two prime water-scarce environments: spaceships and urban areas. Though resistance to wastewater reuse is mostly psychological, citizen’s disgust is balanced by three realities:
- Many cities practice de-facto wastewater reuse, as long as there is a city upstream of theirs.
- Advanced technological treatment, comprising of physical barriers (filtration, reverse osmosis), chemical disinfection (hydrogen peroxide), and ultraviolet disinfection, can achieve an effluent water quality often far superior to local water quality.
- Severe water scarcity and depleted groundwater aquifers leave cities with few choices of water supply.
These facts have tipped the balance in places like Orange County, CA, which is recharging its groundwater supply with 70 million gallons per day of reclaimed water; Singapore, where 15% of the water is recycled; and Windhoek, Namibia, the only city in the world that directly uses treated wastewater for drinking.
Using wastewater as a water supply resource has implications for the modernization and sustainability of cities. It challenges conceptions of the modern city – as a place connected miraculously and invisibly to endless natural resources, and as an aesthetic place – but does so through technological advancement, also a hallmark of modernity. But perhaps more importantly, drinking wastewater re-conceptualizes waste as a resource, and in so doing, re-conceptualizes the city.
Cities were once built as importers and exporters: importing natural resources and exporting waste. But wastewater recycling is a step towards the closed loop resource use of the past, when the products of a small human population and limited consumption could be easily assimilated by the planet, and of self-sustaining natural ecosystems (You can read about resource flows through a cherry tree in William McDonough and Michael Braungart’s Cradle to Cradle). The highly technological city of the future might be taking a cue on sustainability from the past.