The Australian urban water sector faces a significant challenge: energy use is expected to grow to 200-250% of 2007 levels by 2030. However, Australia aims to reduce greenhouse gas emissions 80% below 2000 levels by 2050. To contribute proportionately, the water sector would need to reduce the projected energy demand in 2030 by 85%, or reduce the carbon-intensity of its energy by the same amount.
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-related energy 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.
The first objective of this thesis was to understand the current energy impact of water supply and use in cities. Particular attention was given to indirect water-energy links because they are large, and under-examined. A conceptual model of all known links was developed and populated for an average city of one million Australian people. This demonstrated that water-related energy accounted for 13% of the total electricity and 18% of the natural gas use. Collectively, this represented 9% of the primary energy use or 8% of total national greenhouse gas 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 energy use of Australian agriculture.
Residential water use accounted for 45% of water-related energy in cities. Industrial and commercial water-use contributed 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 Mathematical Material Flow Analysis model was developed to describe household flows of water, electricity, natural gas, and related greenhouse gas emissions and costs. Simulation of the current state of an existing household was validated with three years of independently monitored data from utility records. Key factors of influence, and uncertainties were quantified. Water-related energy accounted for 59% of household energy use (excluding transport), and 35% of household greenhouse gas emissions. The shower, clothes-washer and bath sub-systems comprised the majority of water-related energy use. The clothes-washer, dishwasher and electric kettle comprised the majority of water-related greenhouse gas emissions.
Detailed scenarios investigated the impact of changes. For the household evaluated, improvements in technology, without changing to a solar hot water system, result in less than a 15% reduction in energy use and greenhouse gas emissions. In contrast, combined behavioural and technical changes have a much higher potential. The simulations also demonstrated that some water-saving technologies, such as installation of energy-efficient clothes-washers, could increase greenhouse gas emissions, if it shifted energy consumption from natural gas, to coal-fired electricity.
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 made visible large volumes of rainwater, stormwater, and evapo-transpiration which are typically ignored and unaccounted in current reporting. From the balance, quantitative indicators of the hydrological performance of the city were derived. These highlighted large inter-city variability. The mass balance demonstrated high value with regard to urban water accounting, monitoring and management. This has wide implications for designing and managing cities to increase water harvesting within the city.
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. These themes were subsequently quantified for relative potential and effort to create a roadmap articulating a staged program. Priority elements 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 greenhouse gas emissions, and (iv) improved understanding and management of customer motivations.
This thesis shows how urban water management influences a sizable proportion of Australia’s energy use. It demonstrates the importance of understanding households as a primary source of influence. It provides a systematic methodology to explore, understand and manage water-related energy in cities. It shows how aspects of the urban metabolism framework may be used to derive quantitative indicators of performance and drive accuracy into reporting systems.
Collectively, the work provides a new way of looking at the influence of water management in cities. It is possible that the understanding will 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 highly valuable in a future of water shortages and carbon caps.