The Energy-Water Nexus and Urban Metabolism
Published on by Water Network Research, Official research team of The Water Network in Academic
Between 2005 and 2007, five major Australian cities faced crisis-level shortages of water. Headlines warned of "Armageddon". Cities had to "desalinate or die"1,2. Climate change was widely held responsible3-5. The crisis spawned a significant surge in urban water infrastructure investment growing from a record AU$2.4billion in major cities alone in 2004-05 to over $14 billion in 2008-2009. Between 2008 and 2013, rainfall alleviated water shortages and investment pressure. However, a new challenge has emerged.
The energy demand for water in Australian cities is anticipated to grow to 200-250% of 2007 levels by 2030. An increase in energy use for urban water supplies is one problem. But when this increase in energy is added to an expected rise in electricity costs ($/MWh), the energy bill for urban water is anticipated to increase around six-fold for most Australian states8. This now represents a significant business risk to the Australian water sector9. Ultimately, these costs have to be incorporated into water prices and passed on to consumers.
To compound the challenge, in December 2007 Australia ratified the Kyoto Protocol. This established a national long-term goal to reduce greenhouse gas (GHG) emissions 80% below 2000 levels by 2050 (Australian Government Department of Climate Change and Energy Efficiency 2012). This means that if the water sector was to contribute proportionately, then energy use for urban water must be reduced by more than 90% from the projected 2030 levels. Alternatively, an equivalent cut to the GHG emissions of the energy sources traditionally relied upon needs to be achieved.
The problem is not isolated to the water sector: our cities, their buildings, and their management are all part of the challenge. A lack of quantitative information regarding water-energy links has constrained the motivation and solutions. However, there is substantial opportunity for action. Understanding the nexus, or connection between water and energy, is the key.
Analysis by The Urban Water Security Research Alliance
In 2007 theUrban Water Security Research Allianceformed to address South East Queensland's (SEQ's) urban water issues. The Alliance delivered significant research (including 109 technical reports, 50 peer reviewed papers, four Science Forum proceedings and six books published in five years) addressing myriad water issues, including a range of energy, greenhouse gas and cost-related research.
One PhD project10focussed on understanding water-energy links in cities, and the related analytical framework of urban metabolism.
The first objective of the PhD research was to understand the current energy influence of water supply and use in cities. Particular attention was given to understanding not only the direct energy consumed by water and wastewater services in cities, but also the indirect influence of water use in cities. Indirect water-energy links were the focus because they are large and relatively poorly studied. Analysis of the "average Australian city" of one million people demonstrated that water-related energy accounted for 13% of the total electricity and 18% of the natural gas used in Australia in 2006-2007.
Collectively, this represented 9% of the primary energy use and 8% of total national GHG emissions. Water-related energy in cities is equivalent to one-third of the total energy use of all Australian industry (excluding transport); it is equal to approximately half the energy usage of the Australian residential sector; and it is over four times the direct energy use of Australian agriculture (excluding embodied energy use). Residential water-use accounted for 45% of water-related energy in cities, with industrial and commercial water-use accounting for another 41%. The balance was comprised of utility energy use, energy related to carbon and nutrient loss, and the "water component" of the urban heat island effect.
The second objective sought to understand and quantify water-related energy in households. A detailed model was developed to describe household flows of water, electricity, natural gas, and related greenhouse gas (GHG) emissions and costs12. The model was structured so that either an individual household could be simulated, or a collection of household types (ie, a city) in aggregate. Simulation of the current state of an existing household showed that water-related energy accounted for 50% of household energy use (excluding transport), and 35% of household GHG emissions. The shower, clothes-washer and bath sub-systems comprised the major share of water-related energy use. The clothes-washer, dishwasher and electric kettle comprised the bulk of water-related GHG emissions.
Detailed scenario simulations investigated the impact of changes to technologies and behaviours within the household. Improvements in technology commonly available at the time, without changing to a solar hot water system, result in less than a 15% reduction in energy use and GHG emissions. In contrast, combined behavioural and technical changes had much greater potential. For example, with all realistic possible behavioural and technical changes (including installation of a solar hot water system and altered plumbing to maximise the use of solar water heating in clothes washers and dishwashers), water-related GHG emissions could be reduced to 12% of the baseline in the "realistic" and water-related energy to 26% of baseline.
The simulations also demonstrated that some technologies, such as installation of a water-efficient clothes-washers, could increase GHG emissions if it shifted the energy source for heating the water. This could occur, for example, if a clothes washer which drew on hot water from a hot water system (heated with natural gas or solar energy) was replaced with a new, water-efficient clothes washer which had only a cold water inlet. As a consequence, the new machine would rely on electricity to heat the water internally within the machine. As the majority of electricity supplied in Australia is sourced from coal-fired stations (with around 1 kg CO2-e per kWh. In contrast solar-heated hot water has a lower emissions intensity, and the Australian government rates natural gas as contributing 0.197 kg CO2-e per kWh.
The third objective aimed to develop, apply and explore an aspect of urban metabolism theory with regard to our understanding of water flows in cities. A mass balance representing all anthropogenic and natural urban water flows was developed and populated for four Australian cities. The mass balance exposed large volumes of rainwater, stormwater and evapotranspiration, which are typically ignored and unaccounted for in current reporting. Flows that were ignored and unreported in major cities despite those cities facing major water crises. Using the mass balancing approach, quantitative indicators of the hydrological performance of the city were derived. The mass balance approach proved to be very valuable in terms of urban water accounting, monitoring and management. This has widespread implications for designing and managing cities to increase water harvesting within the urban system13.
The fourth objective was to define research priorities for systematic management and policy formulation regarding water-related energy in cities. An international workshop was convened with diverse representation. Facilitated discussion identified a vision for successful cities as well as relevant opportunities and barriers. Themes of necessary work were identified using the World Café method - a meeting process designed to identify and elicit a degree of consensus from diverse stakeholders about complex issues. The identified themes were ranked by participants to help quantify the potential of each initiative and the anticipated effort necessary to undertake it. This enabled the author to create a roadmap articulating a staged program which could begin with the easier, higher-impact measures; the low-hanging fruit. Priority elements in the road map for improved management of water-related energy include: (i) combined standards, guidelines and funding for water and energy efficiency; (ii) development of educational programs; (iii) methods to quantify and track water-related energy and GHG emissions; and (iv) improved understanding and management of customer motivations14.
Collectively, this research demonstrated how urban water management influences a sizable proportion of Australia's energy use. Understanding households was found to be of primary importance and influence. The work showed how one aspect of an urban metabolism framework could be used to (a) systematically account for water and ( b ) derive quantitative indicators of performance and drive accuracy for reporting systems. The results provide key insights to help water and city managers create better plans for our cities - plans that solve problems at the core, rather than shifting them from one domain to another. This is anticipated to be of great value in a future of water shortages, rising energy costs, and more stringently applied carbon targets.
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- Research
- Integrated Urban Water Management