Editorial Perspectives: bringing the energy–water nexus home to promote conservation and efficiency

Residential buildings – homes – are the places we can be ourselves, where we let down. We spend 70% of our lives at home, and our homes and our behaviors are unique. We wash and dry the laundry. We adjust the thermostat. We set the shower to just the right temperature. A combination of home infrastructure and human behaviors determine our residential water and energy consumption.^1,2 While many studies have quantified energy and water systems on large scales (e.g., ref. 3–5), the home remains an underexplored yet important aspect of the energy–water nexus.⁶

Reducing residential energy and water consumption are among the strategies proposed for climate mitigation and adaptation. Conservation and efficiency are two ways to reduce household consumption, with conservation typically achieved through behavior change and efficiency stemming from infrastructure upgrades. For example, I can save water by installing a low-flow dual-flush toilet (efficiency) and reducing the number of times I flush (“If it's yellow, let it mellow”; conservation). Yet sometimes these decisions can be difficult. We were recently faced with a broken air conditioner in our home. The least expensive option (around $7100) was a single-stage air conditioner with a seasonal energy efficiency ratio (SEER) rating of 13, the federal minimum (a higher SEER rating is more efficient). The most expensive option (around $12 500) was a two-stage air conditioner, which was better suited for our house, with a SEER rating of 21. We ended up selecting the more efficient unit, but not without significant pause at the larger financial investment. These tough efficiency decisions are financially out of reach for many households, regardless of the payback from energy and/or water savings. Despite long-term economic feasibility, efficient home appliance investments often require continued rebate or subsidy programs to encourage adoption and broader accessibility. At the same time, federal standards need periodic revision to promote more efficient appliances on the market.

While conservation and efficiency can be a win–win, some approaches can present challenging tradeoffs with human health when we fail to consider the whole home system. Better sealing of the building envelope through weatherstripping and insulation can reduce energy consumption, but these efficiency gains can introduce indoor air quality challenges due to fewer air exchanges.⁷ Water conservation and low-flow fixtures reduce water consumption while also increasing stagnation time within premise plumbing, potentially leading to poor water quality and risk of exposure to contaminants (e.g., lead, copper) and pathogens (e.g., Legionella pneumophila).⁸ Leveraging research on the “human exposome”,⁸ more studies are needed on balancing energy and water efficiency through infrastructure upgrades with suitable indoor environmental quality for a healthy residential environment. Beyond basic research, we as a community of experts should also translate our fundamental science into applied knowledge through engagement with industry, standards organizations, and government to better inform products and policies at the residential scale.

Understanding and managing the impacts of conservation and efficiency requires measuring water and energy consumption data. This measurement typically comes from electricity, natural gas, and water meters, with advanced technologies presenting new opportunities for resource management. Many energy utilities have installed “smart” meters capable of better measurement with automated data collection. Several water utilities are following this example. Data from these “smart” meters can help utility managers and researchers better understand energy and water end uses.^9–11 For example, how much energy is used for water heating? Does a particular subdivision have above-average water leaks? How much water and energy might low-flow showerheads save? Data-driven answers to these questions can inform conservation and efficiency programs.

New metering approaches can also provide feedback to occupants. Real-time feedback has been shown to reduce resource consumption by 1–5%. A study of real-time shower feedback in Swiss hotels showed an 11% reduction in energy consumption.¹² These results are promising, showing that we can change our behaviors in response to feedback, even in a hotel setting where we don't pay for utilities directly. Yet we still have more to learn. How might real-time feedback at home change our behaviors? How do “smart” meters change the Hawthorne effect, where occupants change their behavior in response to being monitored? How does motivation to reduce consumption change over time? With increased “smart” meter installations, additional controlled studies can answer such questions to quantify the water, energy, and/or emissions reductions from behavior responses to real-time feedback.

Looking ahead, residential energy and water data can inform efficiency investments and encourage conservation efforts at home. More research work remains, in particular:

• Closing the balance: mass and energy balance calculations, formulated for the home, can quantify flows of water and energy to specific end uses, including water leaks and standby power loads. By understanding the amount of water and energy consumed for different purposes, we can better encourage conservation behavior, incentivize upgrading inefficient appliances, locate and fix leaks, and develop technologies to inform occupants. Using data to inform these changes can also help quantify resource (and possibly monetary) savings in response to interventions, potentially motivating continued efficiency investments.

• Managing risks: changing water quality and indoor air quality can present risks to human health. Conservation and efficiency measures should promote both broader social well-being and individual well-being through healthy indoor environmental quality. Research has a role to play in understanding the fundamental science of humans in the indoor environment, and also translating that science into applied knowledge and action through policies and residential building standards.

• Taking personal responsibility: the social sustainability of water and energy savings depends on the actions of many individuals. Effectiveness of resource conservation and efficiency requires studying the humans themselves, including motivations, empowerment, and personal action. We must also remember that we are humans too. Our personal actions as environmental experts can affect our perceived credibility and public support for science-informed policies. A recent study showed that people are more likely to support climate policies if the one advocating for said policies has a low personal carbon footprint.¹³ We too should “walk the talk” and take shorter showers, adjust the thermostat, and invest in the more efficient air conditioner despite the cost.

Data-driven approaches can promote managing energy and water resources by first measuring residential consumption: understanding where, when, and how humans use energy and water at home. Yet data on their own are not enough. Our work also has to consider human behavior, policy structures, and residential standards, using science to inform energy and water efficiency together in a healthy residential environment. Putting the human at the center of conservation and efficiency efforts could enable lasting change.¹³ After all, if we want to create a sustainable future, it makes sense to start at home.

References

1. S. Z. Attari, Perceptions of water use, Proc. Natl. Acad. Sci. U. S. A., 2014, 111(14), 5129–5134.
2. S. Z. Attari, M. L. DeKay, C. I. Davidson and W. B. de Bruin, Public perceptions of energy consumption and savings, Proc. Natl. Acad. Sci. U. S. A., 2010, 107(37), 16054–16059.
3. K. T. Sanders, Critical Review: Uncharted Waters? The Future of the Electricity-Water Nexus, Environ. Sci. Technol., 2015, 49(1), 51–66.
4. E. Grubert and K. T. Sanders, Water Use in the United States Energy System: A National Assessment and Unit Process Inventory of Water Consumption and Withdrawals, Environ. Sci. Technol., 2018, 52(11), 6695–6703.
5. C. M. Chini and A. S. Stillwell, The State of U.S. Urban Water: Data and the Energy-Water Nexus, Water Resour. Res., 2018, 54(3), 1796–1811.
6. C. M. Chini, K. L. Schreiber, Z. A. Barker and A. S. Stillwell, Quantifying Energy and Water Savings in the U.S. Residential Sector, Environ. Sci. Technol., 2016, 50(17), 9003–9012.
7. B. Stephens, E. M. Carter, E. T. Gall, C. M. Earnest, E. A. Walsh, D. E. Hun and M. C. Jackson, Home Energy-Efficiency Retrofits, Environ. Health Perspect., 2011, 119(7), 283–284.
8. D. Dai, A. J. Prussin II, L. C. Marr, P. J. Vikesland, M. A. Edwards and A. Pruden, Factors Shaping the Human Exposome in the Built Environment: Opportunities for Engineering Control, Environ. Sci. Technol., 2017, 51(14), 7759–7774.
9. J. S. Vitter and M. E. Webber, A non-intrusive approach for classifying residential water events using coincident electricity data, Environ. Model. Softw., 2018, 100, 302–313.
10. A. Cominola, M. Giuliani, D. Piga, A. Castelletti and A. E. Rizzoli, Benefits and challenges of using smart meters for advancing residential water demand modeling and management: A review, Environ. Model. Softw., 2015, 72, 198–214.
11. A. Cominola, E. S. Spang, M. Giuliani, A. Castelletti, J. R. Lund and F. J. Loge, Segmentation analysis of residential water-electricity demand for customized demand-side management programs, J. Cleaner Prod., 2018, 172, 1607–1619.
12. V. Tiefenbeck, A. Wörner, S. Schöb, E. Fleisch and T. Staake, Real-time feedback promotes energy conservation in the absence of volunteer selection bias and monetary incentives, Nat. Energy, 2019, 4(1), 35–41.
13. S. Z. Attari, D. H. Krantz and E. U. Weber, Climate change communicators' carbon footprints affect their audience's policy support, Clim. Change, 2019, 154(3–4), 529–545.

---