Urban Water Systems Research Articles

Green Infrastructures for Urban Water System: Balance between Cities and Nature

Urban water systems face severe challenges such as urbanisation, population growth and climate change. Traditional technical solutions, i.e., pipe-based, grey infrastructure, have a single purpose and are proven to be unsustainable compared to multi-purpose nature-based solutions. Green Infrastructure encompasses on-site stormwater management practices, which, in contrast to the centralised grey infrastructure, are often decentralised. Technologies such as green roofs, walls, trees, infiltration trenches, wetlands, rainwater harvesting and permeable pavements exhibit multi-functionality. They are capable of reducing stormwater runoff, retaining stormwater in the landscape, preserving the natural water balance, enhancing local climate resilience and also delivering ecological, social and community services. Creating multi-functional, multiple-benefit systems, however, also warrants multidisciplinary approaches involving landscape architects, urban planners, engineers and more to successfully create a balance between cities and nature. This Special Issue aims to bridge this multidisciplinary research gap by collecting recent challenges and opportunities from on-site systems up to the watershed scale.

A Critical Review of Extraction and Identification Methods of Microplastics in Wastewater and Drinking Water.

This critical review analyzes methodologies used to collect, quantify, and characterize microplastics in both wastewater and drinking water. Researchers used different techniques at all stages, from collection to characterization, for quantifying microplastics in urban water systems. This represents a barrier to comprehensively assess the current loads of microplastic and to compare the results obtained by such assessments. The compiled studies address microplastic contamination using four types of sample collection techniques, four methods for processing samples, and four techniques for characterizing microplastics. This results in significant discrepancies in each of the following: (1) reported concentrations in both wastewater effluents and drinking water, (2) microplastic characteristics (i.e., size, color, shape, and composition), and (3) quality control and assurance procedures. Finally, this review qualitatively evaluated the reports by the completeness of their data based on a ranking system using five criteria: sample collection, sample processing, quality control, identification technique, and results. The results of this ranking system clarify disparities between the studies.

Correction to: Developing a Model for Decision-Makers in Dynamic Modeling of Urban Water System Management

The original version of this article unfortunately contains mistakes introduced during the publishing process.

Characteristics of organic pollutants in source water and purification evaluations in drinking water treatment plants

The release of contaminants of emerging concern (CECs) into water bodies has aroused wide concern in recent years. Little information on the characteristics of CECs to pose potential risks even at low concentrations in urban water systems of Shanghai is available. This study investigated the occurrence and spatial distribution in source water, as well as the fates by drinking water treatment processes for organic compounds including 35 pesticides, 17 antibiotics, 7 microcystins (MCs), and 10 disinfection by-products (DBPs). The similar trends across seasons for COD and TOC, the indicators for organic pollutants, indicated that the water qualities in three targeted reservoirs were relatively stable. COD in the R3 reservoir inlet was 1.3-2.4 times greater than that in the R1 and R2 reservoirs, possibly resulting from the inflow of the Taipu River as a tributary. Pesticides, particularly methamidophos and metabolites, macrolide and sulfonamide antibiotics, particularly roxithromycin, were frequently detected in Shanghai source water inlets. Pesticide concentrations were 2.58–3.66 μg/L much higher than antibiotics (8.6–47.6 ng/L). The results showed that MCs (ng/L) and DBPs (haloacetic acids, HAAs μg/L; N-nitrosodimethylamine, NDMA ng/L) were found to be in low detection frequencies. It was found that 51.1-74.6% of organic matters in source water were composed of molecular weight (MW) <1 kDa. The removal rates for the part of MW <1 kDa were only 11.7–12.3% through the conventional treatment processes, compared with higher removal rates of 23.5–28.5% by advanced treatment processes. Pesticides, antibiotics and MCs can be significantly removed by six drinking water treatment plants.

Water and ancient cities: Urban supply systems

Water supply is widely recognized as one of the greatest challenges to urban living today. Whether negotiating shortage or excess, securing and sustaining a reliable supply of water for human consumption, health and sanitation, processing and manufacturing of goods, and all other aspects of life is a complex undertaking in urban contexts. To complicate provision even further, sources and resources of water are diverse, change over time, and interact with and are influenced by complex biophysical and cultural processes. People have been living in cities for millennia and across very different environments: from the earliest urban centers of the Near Eastern arid lands to the market towns growing along waterways and wetlands of northern Europe to mention but two profoundly different cases. How did ancient cities obtain water? What was water needed for? To inform these questions, we have curated a collection of articles that address how ancient urban societies have dealt with water, securing supply and negotiating changes over time across a wide spectrum of cultures, environments, and periods of time. Within the wide range of articles offered by WIREs Water to date, our selection currently presents case studies that illustrate different regional and cultural contexts for two main reasons. First, we want to illustrate the sheer diversity and complexity of past water–city interactions, with a focus on the creativity, dynamism, and flexibility expressed by historical water supply systems. Second, we aim to expose some of the links between opportunities and challenges shaping the water–city interplay over the long term. In our globalized world, urban living is characterized by increasing speed in the way we operate, relate to our surroundings, and satisfy our needs. Modern urban water supply is largely dependent on pipeline provisioning for fast and reliable delivery. While this collection does not explore the contribution of historical developments to issues concerning present and future urban water systems, we hope that the articles presented will inspire thinking beyond our times and reflecting on how past urban societies have secured water provision over the long term. Featuring profoundly different historical developments, the case studies in this collection illustrate some general threads running across three main topics. Local environmental conditions have played a critical role not only in shaping approaches to and maintenance of past water management strategies but also in the spatial organization of the urban settlement. For the same services, chiefly water supply to the urban population, ancient societies developed adaptive strategies that appear tailored to their environments. This is clearly demonstrated in the examples from Mesopotamia (Altaweel, 2019) and Mesoamerica (Chase & Cesaretti, 2018; Mejía Ramón & Johnson, 2019) that show how water supply was organized across urban landscapes, whereby conditions in the hinterlands had direct implications for the central areas and vice versa. A second main theme emerging from this collection is the sheer diversity of strategies used by past societies to secure water and negotiate scarcity or excess and conditional changes in social, environmental, and economic development. Firmly embedded and operating within urban landscapes, as illustrated above, ancient cities had several, often integrated ways to tap water from multiple sources and distribute it. We tend to consider rainfall as the main, if not the only, source of water for cities that have no immediate access to freshwater (surface) bodies. However, there are ample examples of past water systems integrating the management of groundwater reserves, water catchment stability, and soil moisture together with capturing and storing technologies to secure water supply for subsistence, food production, and resource processing. This is particularly well illustrated by examples from the Jordan desert (Raja & Lichtenberger, 2019), the Mediterranean island of Sardinia (Cespa, 2018), and Scandinavia (Poulsen & Gundersen, 2019) where ancient urban societies turned challenges into opportunities by developing a wide range of waterworks and solutions. A third, equally important aspect concerns how water availability, management, and changes shape societal power structures, behaviors, and belief systems. Control over, and access to, water determines the survival of people, species, and habitats, as we learn from the ancient cities in pre-Columbian North America (Baires, 2015), Maya Belize (Lucero, Harrison, Larmon, Nissen, & Benson, 2016) and medieval south Italy (Jäckh, 2019), where urban water availability and provision are intertwined with wealth, power, and prestige. These case studies show the intangible, often hidden influence of water on cultures, processes of decision-making and social relations, and the underlying mechanisms of adaptation in urban contexts. Water and Urban Landscapes Managing Urban Water Valuing Water and Urban Cultures

The importance of system configuration for distributed direct potable water reuse

Water and wastewater infrastructure worldwide faces unprecedented demand and supply conflicts that require unconventional solutions. In this study, we develop a novel modelling framework to assess the environmental and economic implications of a hybrid water supply system that supplements a centralized surface water supply with distributed direct potable reuse (DPR) of municipal wastewater, as a strategy to address such challenges. The model is tested with real water and wastewater systems data from the City of Houston, Texas. Results show that supplementing the conventional centralized water supply with distributed DPR would reduce water age in the drinking-water distribution network and hence improve water quality; properly designed system configurations attain system-wide net energy savings even with the high energy consumption of existing technologies used for advanced treatment of the wastewater. A target energy efficiency for future advanced treatment technologies is identified to achieve net energy saving with all hybrid system configurations. Furthermore, distributed DPR remains financially competitive compared with other unconventional water supply solutions. The modelling framework and associated databases developed in this study serve an important research need for quantitatively characterizing distributed and hybrid water systems, laying the necessary foundation for rational design of integrated urban water systems. Water and wastewater infrastructure worldwide faces unprecedented challenges. A new model can assess the environmental and economic implications of a hybrid water supply system that provides a centralized surface water supply with distributed direct potable reuse of municipal wastewater.

PIE Index: Quantifying Stakeholder Engagement on Urban Water System Projects and Initiatives

AbstractRecent water crises showed that excluding community stakeholders in urban water system decision-making throughout can have an adverse effect on the entire community and decrease system resi...

On the Use of an IoT Integrated System for Water Quality Monitoring and Management in Wastewater Treatment Plants

The deteriorating water environment demands new approaches and technologies to achieve sustainable and smart management of urban water systems. Wireless sensor networks represent a promising technology for water quality monitoring and management. The use of wireless sensor networks facilitates the improvement of current centralized systems and traditional manual methods, leading to decentralized smart water quality monitoring systems adaptable to the dynamic and heterogeneous water distribution infrastructure of cities. However, there is a need for a low-cost wireless sensor node solution on the market that enables a cost-effective deployment of this new generation of systems. This paper presents the integration to a wireless sensor network and a preliminary validation in a wastewater treatment plant scenario of a low-cost water quality monitoring device in the close-to-market stage. This device consists of a nitrate and nitrite analyzer based on a novel ion chromatography detection method. The analytical device is integrated using an Internet of Things software platform and tested under real conditions. By doing so, a decentralized smart water quality monitoring system that is conceived and developed for water quality monitoring and management is accomplished. In the presented scenario, such a system allows online near-real-time communication with several devices deployed in multiple water treatment plants and provides preventive and data analytics mechanisms to support decision making. The results obtained comparing laboratory and device measured data demonstrate the reliability of the system and the analytical method implemented in the device.

Constrained optimization model of the volume of initial rainwater storage tank based on ANN and PSO.

Rainfall runoff pollution is one of the main causes of water quality deterioration in urban water system. Setting up initial rainwater storage tank could be one of the rapid and effective methods to control runoff pollution. In order to speed up the water environment management processes, the Chinese government has adopted the Public-Private-Partnership (PPP) mode in the water environment treatment to deal with the shortage of funds. Ensuring water quality and controlling water environment management cost are key to PPP projects. Therefore, factors such as pollutant accumulation characteristics of the catchment, land space availability, sewage treatment plants capacity, and river water management cost should be considered during the design of the initial rainwater storage tank on the premise of ensuring water quality. The empirical design method can hardly meet these requirements simultaneously. Under the background of PPP water environment treatment project, a constrained economic optimization model of the initial rainwater storage tank was presented in this paper. The relationship between the total cost of the water environment management and the interception rate of the initial rainwater storage tanks was established by means of Artificial Neural Network (ANN), while the penalty function was used to transform the constrained optimization problem into an unconstrained optimization problem. The interception rate of the initial rainwater storage tanks was then optimized by means of Particle Swarm Optimization (PSO), and the designed volume of the storage tanks was calculated according to the relationship between the interception rate of the storage tank and the cumulative runoff of the related catchment. Finally, a case study of a PPP demonstration project in a plain city in China was conducted. The results demonstrated that compared with the specification method, the total volume of the initial rainwater storage tank increased by 38.7%, the interception rate increased by 68.4%, and the total cost of river water treatment decreased by 5.7% under the constraints of land space availability and sewage treatment capacity. In addition, the optimized method proposed in this paper could reflect the pollutant accumulation characteristics of the catchment. It not only reduce the total cost of the water environment management but also effectively reduce the impact of non-point source pollution on urban water system, and could be more widely used in other areas and PPP projects.

A Research Agenda for the Future of Urban Water Management: Exploring the Potential of Nongrid, Small-Grid, and Hybrid Solutions.

Recent developments in high- and middle-income countries have exhibited a shift from conventional urban water systems to alternative solutions that are more diverse in source separation, decentralization, and modularization. These solutions include nongrid, small-grid, and hybrid systems to address such pressing global challenges as climate change, eutrophication, and rapid urbanization. They close loops, recover valuable resources, and adapt quickly to changing boundary conditions such as population size. Moving to such alternative solutions requires both technical and social innovations to coevolve over time into integrated socio-technical urban water systems. Current implementations of alternative systems in high- and middle-income countries are promising, but they also underline the need for research questions to be addressed from technical, social, and transformative perspectives. Future research should pursue a transdisciplinary research approach to generating evidence through socio-technical "lighthouse" projects that apply alternative urban water systems at scale. Such research should leverage experiences from these projects in diverse socio-economic contexts, identify their potentials and limitations from an integrated perspective, and share their successes and failures across the urban water sector.

Study on Strategy Planning of Sponge City Construction in Guizhou Province from the View of Resilient City

In recent years, extreme weather is constantly emerging on a global scale. Excessive development and construction of cities has changed the original water systems of citys, and lead to urban water hazards and water environment deterioration. Since 2014, after China has been vigorously promoting the plan of sponge city and relative construction, the problems of urban water systems gradually get relieved. By introducing the concept of resilience in this study into the development of sponge city planning strategies, a comprehensive and systematic top-level design of sponge city planning and construction is made from the four dimensions of ecological resilience, engineering resilience, economic resilience and social resilience. At the same time, combining with the issues in existing pilot sponge urban planning and construction process such as the lack of systematicness, integrality, fragmentation etc., based on the study case of pilot sponge city - Guiyang city in Guizhou province, with the resilience concept as the guidance, it is presented in this study the planning strategies of sponge city ecological pattern developing, systematic planning and construction guidance, and explored the extended industrial development of sponge city and the construction control mechanism, trying to provides a new way of thinking and a new approach of sponge city planning and construction related research.

An unintended challenge of microplastic pollution in the urban surface water system of Lahore, Pakistan.

Plastics are widely considered to be a major threat particularly in the urban areas owing to extensive use of plastic products. The current study is the first investigation to highlight the microplastics (MPs) pollution from the freshwater (Ravi River) located in the predominant urban center, i.e., Lahore, Pakistan. The concentration profile was quantified from surface water (n = 19) and sediments (n = 19) collected from different drains and canals of predominant freshwater resources in Lahore, Pakistan. The highest content of MPs was observed in the sullage carrier with mean concentration of 16,150 ± 80 MPs/m3 and 40,536 ± 202 MPs/m2 in the water and sediments respectively. The lowest level was detected in the link canals with mean concentration of 190 ± 141 MPs/m3 in the water and 683 ± 479 MPs/m2 in the sediments. The proportion of large size MPs (300μm-5mm) was maximum in the upstream section of Ravi river, whereas fine size MPs (50-150μm) were dominant in the downstream section. In terms of shapes, the fragments were predominant with a relative abundance of 56.1% and 83.1% followed by fibers with a relative abundance of 38.6% and 11.8% in the water and sediments respectively. The chemical composition analysis showed that most of the fibers, fragments, and beads were polyethylene while the sheets were composed of polypropylene. Nevertheless, the foams isolated from the samples were composed of polystyrene. Within 24h, about 2.4 ± 2.4 billion microplastic pieces were estimated to be transported from a single water channel into the river. The highest discharge of MPs was estimated from the sullage carrier with about 7 billion pieces/day.

Exploring the Influence of an Urban Water System on Housing Prices: Case Study of Zhengzhou

A good living environment is the foundation of sustainable housing. Exploring the external influence of environmental factors on housing prices is one of the key issues in the field of real estate research; however, the current study of the urban water landscape on the spillover effect of housing prices is not sufficient. Taking the Zhengzhou residential market as an example, this paper analyzes the effect of an urban water system on residential prices by constructing the traditional Hedonic price model, spatial lag model (SLM) and geographically weighted regression model (GWR) by selecting the main water system and 678 points of residential data in the main urban area. The results show that the accessibility of rivers and lakes and the width and water quality of rivers have a significant effect on residential prices, and the impact of lakes is greater than that of rivers. The spatial heterogeneity of the water system effect is further revealed by adopting spatial lag model and geographically weighted regression model, and the effect of the water system is gradually reduced from the eastern urban area to the western urban area. The results of this study are of great practical significance to the government’s municipal planning, water environment management and housing market management.

Preface

Sustainable Urban Water International Seminar 2019 (SUWIS 2019) has been held successfully on January 24th 2019 at Toyib Hadiwijaya Auditorium in IPB University Dramaga Campus, Bogor, West Java, Indonesia. SUWIS 2019 has bring together the students, lecturers, and researchers in the field of urban water to help fight back the water challenges. This includes mitigation, sustainability and resilience of water issues in developing and developed countries.The SUWIS 2019 theme is mainly focused on Sustainable Urban Water Management as the part of Sustainable Development Goals (SDGs) of United Nation, particularly Goals 6th about water. Presentation of SUWIS 2019 was distributed into four domains as 1) Green Technology for Sustainable Urban Water (GT), 2) Urban Water System and Land Use Change (LU), 3) Socio-Governance Studies on Urban Water (SG), and 4) Sustainable Urban Water Design (UD).We are really thankful to all authors who have contributed high scientific articles to become this proceeding of the SUWIS 2019. We are also grateful to IOP Publishing, especially Anete Ashton (IOP Conference Commissioning Editor), for allowing us to publish accepted peer reviewed papers in IOP Conference Series: Earth and Environment Sciences (EES). We are thankfull to all dedicated reviewers, editors, and assitant editors for finishing reviewing and editing process. And also, for all scientific and organizing committes who have reviewed and encouraged the process to publish 31 arcticles. We also would like to thank Directorate of International Program (ICO) and Graduate School of IPB University, and the Ministry of Research, Technology and Higher Education (Kementerian Riset, Teknologi dan Perguruan Tinggi - RISTEKDIKTI) for supporting us to contribute the World Class University (WCU) agenda.

Life cycle assessment modelling for a developing city‘s water system

The research objective to analysis the urban water system (UWS) includes water treatment and distribution, wastewater collection, treatment, and disposal for Raipur city of Chhattisgarh state in India. The city has a dry tropical climate and a warm summer. Developing city is being under pressure due to rapid population expansion, urbanization and industrialization that causes a considerable change in water resources and their services Using SIMA-PRO LCA technology with ReCiPe and IPCC methods, the environmental impact assessment for the urban water system in Raipur was calculate by conducting a life cycle assessment (LCA). LCA tool focuses on water treatment and supply, wastewater, storm water, energy consumption, emission of pollutants and heavy elements to the water bodies and to sewage sludge and others spatial considerations such as population, economic and social assessment, water quality along with stakeholder engagement. LCA is a useful tool for identifying alternative environmental impact solutions and urban water operation scenarios for future strategic planning. In assessment, we found that water losses in distribution network and electricity consumption in water treatment have highest impact on environment while reducing this two by 15% and 2% then it reduces impact about 16%. We studied the existing conditions and different scenarios in this research to enhance the system’s environmental quality and to find solutions to improve sustainability.

Plants Diversity of Agroforestry System in Ciliwung Riparian Landscape, Bogor Municipality

Ciliwung riparian has facing land use change problem due to settlement occupation, particularly in Bogor which is a municipality with a high population increase in Indonesia. These problem has reduced agroforestry land use of Ciliwung riparian, such as talun (forest garden), kebun campuran (mixed garden), and pekarangan (home garden) which ultimately reduce one of riparian landscape services, that is conserving of plants diversity. Therefore, the purpose of this paper is to show the research result of capacity of conserving plant diversity of agroforestry land use, as a basis for arranging the management of Ciliwung riparian landscape in Bogor Municipality. This study used 14 sample plots of agroforestry land use (4 taluns, 5 kebun campurans, 5 pekarangans) with purposive sampling method, for vegetation analysis of agroforestry land use. Plants diversity was calculated based on value of Shannon-Wiener diversity index (H’) and Margalef richness species index (Dm). The results showed that Ciliwung riparian vegetation in Bogor Municipality was dominated by groundcover plants (0-1 m) and tree plants (5-10 m) with functions as ornamental and conservation plants. The species diversity of agroforestry land use of Ciliwung riparian of Bogor was in medium category (1<H’<3) on average. Kebun campuran has H’ index of 2.07, talun of 1.84, and pekarangan of 1.55. The species richness Dm of talun is 4.32 (high category), while pekarangan and kebun campuran have Dm values in medium category, with values of 3.90 and 3.63 respectively. Overall agroforestry land use of Ciliwung riparian in Bogor Municipality has a good plants diversity (medium-high category), so it can be considered to have fairly balanced ecosystem conditions and medium ecological pressure. This diversity is useful for maintaining the quality and quantity of urban water system in Bogor.

The importance of remnant vegetation coverage along riverbank in supporting urban river naturalization in Bogor City, Indonesia

Human disturbances in urban river landscape and its riverbank cannot be avoided. The construction of buildings and other infrastructure are among the human disturbances which cause a serious decline in urban riverbank quality so that influencing the stability of its landscape ecological cycle. Exploration of vegetated urban riverbank in Indonesia, especially in Bogor City is very important to save its existence in supporting the naturalization of the Ciliwung River. This study aims to estimate the remnant vegetated urban riverbank along the Ciliwung River and estimate the value of landscape/ecosystem services along the riverbank in the Bogor City. This research was carried out by taking four sample locations of the 250 meters and 15 meters wide at the right and the left of the riverbank using aerial photography and processed with ArcGIS software. Then, the land cover delineation and ecosystem services of the four sample locations are estimated by random point sampling method as many as 500 points for each sample location using i-Tree Assessment. The results of this study indicated that vegetation cover along the riverbank in Bogor City is 62% or 300,443 m2 ± 1733.96 m2. The advantages of landscape service for tree vegetation along the Ciliwung riverbank in Bogor City, converted into economic value, is equal to IDR 178,272,333. The landscape ecological function of riparian vegetation has a large role in absorbing pollutant gases in cities, storing carbon in biomass and dust absorption as much as converted into these economic values. Protection and conservation of the remnant vegetated urban riverbank needs to be conducted with various stakeholders so that the value of landscape services can be increased optimally in achieving success of river naturalization for sustainable urban water system in Bogor City.

Analysis of Recharge Area Potential of Upper Cisadane Watershed

This research is being conducted on Upper Cisadane Watershed, Bogor, West Java Province. The aim of this research is to investigate the recharge area and analyze the recharge potential. The data consisted of infiltration rate, slope, soil type, and existing landuse as land unit approach which is collected by purposive sampling. Beside that, climate data were collected to estimate the evaporation. The analysis of the data use SCS-CN method to assess the volume of surface runoff, Penman-Monteith method to asseess the evaporation, and Water Balance Method to asseess the groundwater as the recharge potention. The recharge area would be classified into several areas into the highest to the lowest recharging area. The result of this study would be the total of groundwater fluxas the recharge potential based on each classified recharge area. The condition ofrecharge area could be one of the reasoning in develeoping the urban water system. The land with the good condition has surplus as ΔS=490,26 mm, and the critical one has deficit as ΔS=(-)543,49. The condition of the highest recharghing area would be analysed as the criteria of potential recharging area and the area should be managed well in the future. The condition of the lowest recharghing area would be restored depend on its problem.

Urban water systems: Development of micro-level indicators to support integrated policy.

Urban water systems involve complex interactions between ecological, social and economic factors. Integrated management approaches are needed to achieve multiple policy objectives in the sector and can be pursued at a range of spatial scales. Small-scale integrated water projects are both feasible and valuable in dynamic urban environments in developing countries. This paper develops a method for the prioritization of localities for integrated projects and applies this to the city of Jakarta. A set of indicators is defined following a systems approach, populated, displayed through a dashboard and mapped, and the relationships between indicators are analysed. Indicator-based prioritization allows policy-makers to guide resources to integrated projects to contribute effectively to the achievement of policy goals.

Reducing carbon emissions by integrating urban water systems and renewable energy sources at a community scale

This paper presents a novel take on the energy-water nexus; exploring the coupling of renewable generation sources with drinking water distribution and wastewater collection assets that can store and release energy in response to temporal changes in residential heat demand. The paper presents the development of a simulation tool that uniquely integrates energy storage in drinking water reservoirs, heat recovery from sewers with wind turbine(s), solar photovoltaic panel(s) and a non-renewable source. Simulations at the scale of a 1000 household community and hourly intervals were used to find the optimal energy generation mix that minimises the total annual carbon emissions (embedded and operational). Three different locations in the UK were studied. Results show that the integrated idealised system is able to satisfy the heat demand for up to 63% of the time across a year with no carbon emissions, and reduce the annual associated CO2 by 60% when compared to all heat demand being satisfied by natural gas. This work shows that adopting such an interlinked system at a typical neighbourhood scale could help the UK meet its carbon emission obligations by substantially reducing the 18% of the UK's CO2 emission (currently estimated to be) related to domestic heat use.