Can we make urban water systems more sustainable?

Census data tells us that over 80 per cent of Canada’s population lives in urban areas¹. Further population stress on our cities will place greater pressure on already-constrained water sources and supporting infrastructure. Due to the high costs of building new infrastructure and replacing existing crumbling infrastructure, our large-scale and sometimes centuries-old water systems cannot be upscaled quickly enough to keep pace.

Yet financial aspects are not the only reason for concern, as urban intensification is typically shadowed by strict environmental regulations that prioritize enhancement of the urban water cycle, introduce climate change considerations and urge a gradual transition towards low-carbon communities². It is therefore essential that we take a more objective and environmentally holistic approach to assessing and quantifying long-term sustainability in our urban water systems.

Urban metabolism is a concept and a tool that accounts for the overall flows and fluxes of water, materials, energy, nutrients, chemicals, and wastes into and out of an urban region³ (See Figure 1). Numerous international studies inform us that urban metabolic processes consume the largest amount of global resources and produce enormous waste products, leaving a substantial environmental footprint⁴. Unfortunately, urban water systems are also recognized as a major offender due to water leaks and associated energy losses, and therefore contribute to global unsustainability⁵.

To ensure that every drop of water is mindfully utilized to provide long-term financial stability and environmental sustainability, our planning and design approaches will need to shift from a traditional linear model to a circular metabolic approach (See Figures 2 and 3). The circular metabolic approach represents a resource-efficient and closed-loop method in which once-neglected waste is treated as a new resource⁶.

We can start by considering water sources that are available locally, through reuse of rainfall, stormwater runoff and wastewater produced. These sources employ flexible, autonomous infrastructure that travels shorter distances and has the potential to reduce the overall environmental footprint. It can accomplish this by lowering consumption of materials, energy, and chemicals, saving on build costs, and reducing opportunities for leakage and losses. More specifically, the following four groups of distributed technologies can be applied to supplement existing centralized water infrastructure in achieving a balanced, circular metabolic approach:

1. Water supply and water demand management. Educate users on water conservation, introduce rebate programs, or introduce water restrictions during times of drought.
2. Low-Impact Development (LID) and Green Infrastructure (GI). LID and GI tend to mimic the natural water cycle and thus reduce stormwater runoff volumes, while increasing infiltration into the ground. At the same time, LID and GI have the potential to naturally capture and reduce CO₂. This is achieved with green roofs, rain gardens, permeable pavements, bioretention facilities, or vegetated rooftops.
3. Green buildings. Use high-performing fixtures (such as low-flow toilets, building wastewater recycling, wastewater reuse and rainwater harvesting) to reduce the demand and waste production.
4. Greywater management and onsite wastewater reuse technologies. On-site processing of wastewater can convert organic solids into carbon-rich soil that can be used to support crops, gardens and green spaces. The water that remains can be recycled for non-potable applications, such as toilet flushing, irrigation, and cooling towers.

Implementation While these technologies have been implemented in isolation across Canada, a mindful and integrated approach to urban planning needs to become the norm in order to protect and use our resources most efficiently. Transitioning fully to the circular metabolic approach in the water sector using decentralized technologies is essential to meet growing urban needs and will require major changes in the way we plan, design and fund our infrastructure⁷. These changes will require collaborative leadership from industry, academia and government⁸. We must problem-solve complex urban water issues in creative and sophisticated ways, and work to embed future ready urban water systems across Canada and beyond.

1. Statistics Canada https://www.statcan.gc.ca/eng/start (Accessed February, 2019)
2. Growth Plan for the Greater Golden Horseshoe (2017)
3. P. Baccini, A City’ s Metabolism: Towards the Sustainable Development of Urban Systems. Journal of Urban Technology (1997), 4 (2), 27-39.
4. C. Kennedy, J. Cuddihy, J. Engel-Yan, The Changing Metabolism of Cities. Journal of Industrial Ecology (2007), 11(2) 43-59.
5. C4 https://www.c40.org/about (Accessed February, 2019)
6. The Johnson Foundation at Wingspread. Optimizing the Structure and Scale of Urban Water Infrastructure: Integrating Distributed Systems. Racine, WI: The Johnson Foundation at Wingspread (2014)
7. V. Novotny, J. Ahern, P. Brown, Water Centric Sustainable Communities, John Wiley and Sons, Inc., Hoboken, New Jersey (2010)
8. San Francisco’s Non-potable Water Program A Guidebook for Implementing Onsite Water Systems in the City and County of San Francisco, City of San Francisco, California (2015)