tecnn1ca1 Teatures
resilient designs have survived and science is now uncovering elements of systems design which lead co consistent races of natural resources utilisation per unit of body mass from uni-cellular bacteria right through co the largest organisms such as whales. Looking at our own human body, Tambo (2002) presents another example of a very efficient system chat is pertinen t co the issues facing the water industry at the moment. 'The water inside the human body transports substances and heat, and is disposed o f from che body afrer it has been recycled and re-used about twenty times. This m eans that about 5 per cent of the amount of water inside the body must be replenished with fresh water supplied from outside the body.' Analysing nature from this perspective is achieved by thinking of the metabolism of a system. Urban metabolism is a systems way of looking at the resource inputs and waste outputs of groups. An urban metabolic analysis relies o n measuring the overall water, energy, materials and wastes moving into, out of (and ultimately scored within) a city. This mass-balance of a city "enti ty'' was first proposed by Abel Wolman in I 965 as a means of addressing evident "shortages of water and pollution of water and air". The movement of water, energy and m aterials ch rough cities are all increasingly measured, modelled and importantly verifiable using mass-balance principles. A schematic representatio n of an urban metabolism model is shown in Figure 1. Sustainable directions can be quantified using metabolic analysis by accepting or assuming chat the mass flow of energy, water and materials through a city need co reduce over time - even if the population increases. There are curren tly two principal ways of achieving chis: increased recycling or increased efficiencies. However if technology enabled complete recycling at minimal energy (or CO2 expense) efficiency would be less important. A fundamental challenge for the engineering of future cities and their water systems is co reduce metabolic throughput while improving
liveability and overall ecosystem well-being. The internal layers of our cities such as che infrastructure, economic and governance systems all influence how effectively these materials are used now and how easily our future systems will transition co more sustainable forms. Now let us present how using urban metabolism chinking could potentially refine our urban water services. Knowing the metabolic race of a city helps co understand che relative co ntribution chat a particular policy or sector can make co reducing the metabolic race. For example the water sector could aim co reduce urban dependence on the environment through the provision of water su pply and waste management services through recycling of wastewater or scormwacer or through improving efficiencies. In doing so the metabolism model gives a very tangible and practical way of id entifying co ntributions as organisations or individuals co reducing the metabolic race. Jc also high lights areas chat need the greatest attention or which could most cost-effectively reduce metabolic rate. By creating a co nsistent 'system boundary' for metabolic analysis, a frame of reference will also be created against wh ich the lifecycle of compo nents such as water system s can be viewed. Sustainable cities will require reduci ng our urban metabolism but we also need co recognise this cannot be done by planning for one 'organ' at a rime. For example the water sector is inextricably connected co the energy sector which is connected co p opulation and so on. Using the urban metabol ism m odel, we see the delivery of water as interconnected with greenhouse gas and nutrient emissions. Future city planners and infrastructure designers will not only consider potable water, sewerage and scormwater systems as one but will also consider water, energy and nutrient flows together rather than separately in their outlook plans. In doing chis, systems would be designed with flexibil ity for change rather than as a static independent element. Ultimately our cities and their water systems will be monitored and
benchmarked for their "metabolic efficiency" and their relative draw from and impact on local and global environments. Annual reports will record such m etrics together with the relative contribution chat a particular sector makes co che overall reduction of the coral metabolism of the city. Smart meters may well become fu ndamental measurement cools making transparent water, energy and nutrients flows co operators and co the market place. As we move forward with global carbontrading and local energy and nutrient trading schemes, metabolic analysis will inform the "race of exchange" between these parameters which are necessary fo r che life and future of our cities. In so-doing our systems will make better use of nacural capital, as suggested by Paul Hawken, Amory Lovins and Hunter Lovins in their b ook, Natural Capitalism, and drive systems to configuratio ns better suited and tailored co their local environment. In summary, sustainability wi ll continue co be a very useful concept co advance water services. Leaders in industry will however find new ways of chinki ng that wi ll add to this model and help chem use it in more practical ways and consequently add value co businesses. We believe chat urban metabolism is a key perspective and valueadding way of thinking that can be applied broadly within the water industry.
Acknowledgments The authors acknowledge the support of their respective organisations, Yarra Valley Water and CSIRO (Water For a Healthy Country Program). Help ful review comments from Allen Kearns and Tim Baynes are also acknowledged.
The Authors Francis Pamminger is che Manager of Research and Innovation at Yarra Valley Water, Melbourne, email: francis.pamminger@yvw.com.au; Steven Kenway is a Research Scientist w ith CSIRO Land & Water, Brisbane, email: Steven.Kenway@csiro.au
Journal of the Australian Water Association
water
FEBRUARY 2008 29