A metabolism perspective on alternative urban water servicing options using water mass balance

Urban areas will need to pursue new water servicing options to ensure local supply security. Decisions about how best to employ them are not straightforward due to multiple considerations and the potential for problem shifting among them. We hypothesise that urban water metabolism evaluation based a water mass balance can help address this, and explore the utility of this perspective and the new insights it provides about water servicing options. Using a water mass balance evaluation framework, which considers direct urban water flows (both ‘natural’ hydrological and ‘anthropogenic’ flows), as well as water-related energy, we evaluated how the use of alternative water sources (stormwater/rainwater harvesting, wastewater/greywater recycling) at different scales influences the ‘local water metabolism’ of a case study urban development. New indicators were devised to represent the water-related ‘resource efficiency’ and ‘hydrological performance’ of the urban area. The new insights gained were the extent to which alternative water supplies influence the water efficiency and hydrological performance of the urban area, and the potential energy trade-offs. The novel contribution is the development of new indicators of urban water resource performance that bring together considerations of both the ‘anthropogenic’ and ‘natural’ water cycles, and the interactions between them. These are used for the first time to test alternative water servicing scenarios, and to provide a new perspective to complement broader sustainability assessments of urban water

Urban water security - what does it mean?

This research is focussed on understanding what urban water security means–a surprisingly elusive concept given the global shift from rural to urban living. We first make the case for a distinct urban water security definition. We then identify 25 unique water security definitions, of which three relate to the urban context but all with scope for improvement. Applying novel indices, we assess the prevalence, complexity and evolution of themes and dimensions within all definitions and find a stable spectrum of themes; but note a shifting emphasis towards environmental and social dimensions, away from quality and quantity of supply. Overall the definitions are becoming more comprehensive by simply listing more outcomes to be achieved. Instead of this ‘shopping-list’ approach, we propose a simplified urban water security definition with a focus on agreement of needs with community stakeholders, while using the themes to guide what the objectives might be

Household analysis identifies water-related energy efficiency opportunities

Water heating accounts for around one third of household direct energy use. This energy demand is some four times greater than lighting. Here we use detailed monitoring and modelling of seven individual households to quantify major factors. Using normalized sensitivity results we demonstrate (i) high variability and (ii) a large and consistent influence of shower duration, flow rate, frequency and temperature along with hot water system efficiency, adult population, and the temperature of cold water. A 10% change in these factors influenced 0.1–0.9 kWh/hh-person.d, equivalent to a 2–3% of total household energy use. We draw on 5399 shower events from a further 94 households, and 491 shower temperature measurements to understand the scope for changes to the households. Individual parameters variation guided by these larger datasets demonstrated shower duration and flow rate offer most scope for change. The work helps guide city-scale analysis of household water-related energy demand. It also supports the tailoring of behavioural and technological water-efficiency programs towards those with strongest potential to influence energy. Strong interaction between parameters suggests that programs aiming to influence water-related energy need to be aware of how this interplay either amplifies, or diminishes, the intended energy savings

The effect of water demand management in showers on household energy use

This paper explores the range of potential energy use impacts of shower water demand management in a case study of five highly characterised households in Melbourne (Australia), and assesses the difference in energy and cost responses for four different hot water system types. Results show that a shift to four minute showers (from current durations of between six and ten minutes) would lead to a reduction of between 0.1 and 3.8 kWh p(-1) d(-1) in the households studied, comprising between 9% and 64% of baseline hot water system energy use. Contrasted with an average energy use for water service provision in Melbourne of 0.3 kWh p(-1) d(-1), such household reductions demonstrate significant potential for urban water cycle energy management. Combined water and energy (natural gas) cost savings in response to the four-minute shower scenario were $37 to$500 hh(-1) y(-1) in the households studied. Energy cost savings would be more significant for households with electric storage hot water systems than those with gas systems, at $39 to$900 hh(-1) y(-1), due to higher variable tariffs for electricity than natural gas in Victoria ($0.2678 kWh(-1) vs$0.0625 kWh(-1)). Households with electric storage hot water systems may therefore have greater financial incentive to participate in water-related energy demand management (assuming similar tariff structures). (c) 2017 Elsevier Ltd. All rights reserved

Energy use for water provision in cities

Energy demand for urban water supply is emerging as a significant issue. This work undertakes a multi-city time-series analysis of the direct energy use for urban water supply. It quantifies the energy use and intensity for water supply in 30 cities (total population of over 170 million) and illustrates their performance with a new time-based water-energy profiling approach. Per capita energy use for water provision ranged from 10 kWh/p/a (Melbourne in 2015) to 372 kWh/p/a (San Diego in 2015). Raw water pumping and product water distribution dominate the energy use of most of these systems. For 17 cities with available time-series data (between 2000 and 2015), a general trend in reduction of per capita energy use for water provision is observed (11%–45% reduction). The reduction is likely to be a result of improved water efficiency in most of the cities. Potential influencing factors including climate, topography, operational efficiency and water use patterns are explored to understand why energy use for water provision differs across the cities, and in some cities changes substantially over time. The key insights from this multi-city analysis are that i) some cities may be considered as benchmarks for insight into management of energy use for water provision by better utilising local topography, capitalising on climate events, improving energy efficiency of supply systems, managing non-revenue water and improving residential water efficiency; ii) energy associated with non-revenue water is found to be very substantial in multiple cities studied and represents a significant energy saving potential (i.e. a population-weighted average of 16 kWh/p/a, 25% of the average energy use for water provision); and iii) three Australian cities which encountered a decade-long drought demonstrated the beneficial role of demand-side measures in reducing the negative energy consequences of system augmentations with seawater desalination and inter-basin water transfers

The influence of water on urban energy use

This chapter provides an overview of the diverse and significant links between urban water and energy use. It is motivated by the rapidly increasing energy use in Australian urban water systems with resultant cost and environmental impacts. The chapter identifies opportunities for urban water management in Australia to contribute far more substantially to the reduction of water-related energy use. In particular, this includes energy use for water heating and cooling for residential, industrial, commercial and other purposes. In 2001, water-related energy use in California comprised 19 and 32% of total electrical and natural gas use respectively. Australia is likely to be of similar magnitude. Despite the significance, the connections are poorly understood and largely ignored. This is possibly because many of the influences are indirect, difficult to measure, change regularly and are outside the typical boundary of urban water responsibilities. Additionally, there is a current lack of an overall analytical structure within which to consider, let alone manage, the interconnections. The chapter broadly describes how the water-energy nexus connects to other sustainability issues together with the concept of urban metabolism which is perceived as critical to providing a structure for analysis. Finally, the chapter reflects on future profiles and implications in a future constrained by water and energy simultaneously

How does energy efficiency affect urban water systems?

Urban water management influences significant energy use. In Australian cities, water management directly and indirectly uses 13 % of Australia’s electricity and 18 % of its natural gas. Collectively, it accounted for 8 % of the country’s primary energy use in 2007, approximately five times the direct energy use of the agricultural sector, excluding transport. Water-related energy consumption in cities includes energy used in the provision, consumption, and disposal of water. About 10 % is direct energy use by utilities. The majority of the figure relates to water used in homes, business, and government. There is scope for urban water management to reduce water-related energy use, particularly if strategies actively target the large amount of energy associated with water use. A ‘metabolic’ approach to water mass balance can be used to account for all the inputs and outputs of water flowing through cities. The metabolic balance includes rainfall, stormwater run-off, and percolation to groundwater. It is very distinct to the supply–demand balance typically applied in urban water management. Application of such a balance to four Australian cities in 2004–05, a period of critical water shortage, demonstrated that significant volumes of water passed through them unaccounted for and unused. These unused and untracked local water resources have the potential to provide new supply options; however, they also require substantial efforts to harness effectively. Because urban water systems are completely interconnected with the cities they service, urban water problems cannot be solved in isolation of the city or its planning. Transitioning urban water strategies to become ‘energy sensitive’ therefore has wide implications for urban planning, funding, and management. Likewise, it has other consequences for our cities: wider use, understanding, reporting, and benchmarking of urban metabolism and the water–energy nexus could change how we think about our cities and their water systems. We could actually view our cities as sources of water, and could view our urban water systems as a partial solution to energy and greenhouse gas emission problems. Such thinking could lead to considerable changes in physical systems and institutional structures. As pointed out by Abel Wolman in 1965, there is no shortage of water or energy, but finding new solutions requires long-term thinking