What is urban water recycling?
Of all the Earth’s finite resources, few are as precious as water. All plants and animals need water to survive and thrive. And yet, the availability of water is becoming a serious problem in many parts of the world today, and is a problem that is predicted to grow in intensity in the future. Similar to a sustainable food supply, being able to provide for a sustainable water supply is one of the most critically important functions of a city.
We think that a symbiotic city’s ability to provide for a sustainable supply of water, while at the same time function sustainably within the ecological limits of its bio-region – including the regional water cycle, ground water replenishment, and its critical role support of biodiversity – is a critical part of planning and designing for a Symbiotic City.
To think of water as a finite resource may sound odd. After all, we live on what is often called the “Blue Planet”, where 75% of the Earth’s surface is covered with water. However, most of that water, approximately 97.5% it, is salt water, and is therefore not available for human consumption or agricultural irrigation. And for the small portion of “fresh” water on the planet’s surface, one third of it is locked away in mountain glaciers and polar ice, leaving only approximately 1% of the earth’s water available as potable water. Whether this finite supply of water is sufficient to sustainably meet our species ever-increasing water demands is becoming an increasing important question, and as the human population continues to climb, so too does the rate of water consumption.
A 2011 UNESCO report, the National water footprint accounts: The green, blue and grey water footprint of production and consumption, calculated per capita water footprint by nationality. Water footprint measures the volume of freshwater required to produce a product or deliver a service. The full-cost measurements used in the report take into account the volumes of water consumed and polluted through the entire supply chain. What this report makes very clear is the huge demand our industrialized economies put on water supplies. For example, it takes 600 gallons to make a quarter pound hamburger, and 2,800 gallons to produce a pair of jeans. The Water Footprint of Humanity report by the Water Footprint Foundation shows that the average American consumes 2,060 gallons of water daily. The study pegged the United States’ per capita water footprint at 2,483 m3 per annum – the largest in the world. The majority of the developed world is not much better. Italy, Greece, Canada, Malaysia, and Thailand each have per capita water footprints above 2,200 m3 each year. To put those figures into perspective, the global average water footprint amounts to 1,385 m3 per year.
The good news is that water is recyclable, just like most other resources we extract from our planet. The terms recycled or reclaimed water generally refers to either blackwater – that is water carrying sewage – or process water from industrial processes. Blackwater can easily be recycled through biological means. Probably the most effective method now being used is some variant of the Living Machine or Eco-machine pioneered by John Todd or bacteriological filters like the ones engineered by Waterloo Biofilter Systems. Process water is more complicated, because the recycling process must be specifically designed to remove the types of contaminants. Some combination of physical, chemical and biological recycling may therefore be required.
Recycling water is not new. The sanitation districts in Los Angeles have provided treated wastewater for landscape irrigation in parks and golf courses since 1929. The methods and effectiveness of water treatment processes, however, are continually being refined. For example, Singapore’s reclaimed water, also known as NEWater, has become cleaner than the government issued tap water. Before becoming NEWater, Singapore’s sewage waste water is purified using dual-membrane (via microfiltration and reverse osmosis) and ultraviolet technologies, in addition to conventional water treatment processes. The water is potable and is consumed by humans, but is mostly used by industries requiring high purity water. A world leader in water recycling, Israel treats 80% of its sewage, which amounts to 400 billion litres per year. In Tel Aviv, 100% of the city’s sewage is retreated and used for irrigation. These practices result in less waste, but also provide assurances to farmers who may otherwise be adversely affected by water shortages.
From car washes, to golf course irrigation, to drinkable tap water, the need for reclaimed water is virtually limitless. If effectively integrated into a whole-system economy, our water recycling systems could reasonably be expected to produce a water recycling system to match the naturally-occurring hydrological cycle.
- Recovering Sustainable Water from Wastewater by Audrey D. Levine and Takashi Asano (2004) http://pubs.acs.org/doi/pdf/10.1021/es040504n
- Best sourcing approach keeps water production costs down by Ong Hian Hai and Luc De Ryck (2012) http://www.waterworld.com/articles/wwi/print/volume-21/issue-1/news-highlights/best- sourcing-approach-keeps-water-production-costs-down.html
- The Global Water Footprint Infographic by US Infrastructure http://www.waterfootprint.org/downloads/2010-US-Infrastructure.png
- Water Footprint Network http://www.waterfootprint.org/?page=files/home
- Water Footprint Calculator http://www.waterfootprint.org/?page=cal/WaterFootprintCalculator
- National water footprint accounts: The green, blue and grey water footprint of production and consumption - Prepared for the UNESCO Institute for Water Education by M.M. Mekonnen and A.Y. Hoekstra. (2011) http://www.waterfootprint.org/Reports/Report50-NationalWaterFootprints-Vol1.pdf
- The Water Footprint of Humanity by M.M. Mekonnen and A.Y. Hoekstra (2012) http://www.waterfootprint.org/Reports/Hoekstra-Mekonnen-2012-WaterFootprint-of-Humanity.pdf