Sensitivity Analysis of Using Municipal Boundaries as a Proxy for Service Area Boundaries When Calculating Water Affordability Metrics

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Water is essential for life, and yet one of the nation’s most pressing water challenges has become ensuring that water services are affordable for households and communities. While there has been growing attention and concern around affordable water services, the actual scale of the problem remains poorly understood, in part because of the lack of data availability. The Nicholas Institute’s Water Affordability Dashboard was developed to provide several affordability metrics pulling together publicly available data from different sources: census data, rates data, and digital service area boundaries. As of January 2022, the dashboard provided affordability metrics for over 3,000 utilities located within 10 states, showing that between a tenth to a third of households struggle with affording water services. The ability to understand affordability challenges in other states is limited in states without digital service area boundaries.

Digital service area boundaries are used to identify which communities are served by drinking water and wastewater utilities. A recent inventory by McDonald et al. (2022) shows that over half of the states do not have digital water service area boundaries. This study sought to determine if municipal boundaries could be used as a proxy for service area boundaries when calculating water affordability metrics. We explored several proxy (substitute) geographical boundaries by using different methods to (1) identify municipalities served by water service providers, (2) obtain the digital proxy boundaries (i.e., state provided municipal boundaries or nationally available census places), and (3) account for “outside” service areas for utilities for utilities that charge different rates to customers located outside municipal boundaries (Table ES1).

Four affordability metrics were estimated using five different proxies for service area boundaries across 154 utilities representing a sample of states (California, New Jersey, New Mexico, North Carolina, Pennsylvania, Texas, and Washington), system size (small, medium, medium-large, large, and very large), and ownership type (public and private). There was good correlation (Spearman > 0.95) between affordability metrics using service area boundaries and all proxy geographical boundaries. The overall results indicate that municipal boundaries may serve as a proxy for digital service areas for calculating affordability metrics for public municipal water systems, with a median difference for all affordability metrics within ±0.30% of metrics when calculated using service area boundaries.






Patterson, Lauren, Sophia Bryson and Martin Doyle (2022). Sensitivity Analysis of Using Municipal Boundaries as a Proxy for Service Area Boundaries When Calculating Water Affordability Metrics. Retrieved from



Lauren Patterson


Lauren Patterson joined Duke's Nicholas Institute for Environmental Policy Solutions as a policy associate in October 2013. Her research focuses on changes in average streamflow, floods, and droughts due to climate and human impacts. She has also worked on water utility financing, water transfers between utilities, and drought probabilities. Lauren has an affinity for data analysis and visualization.

Before joining the Nicholas Institute, she contracted at RTI International to provide geospatial and data analysis support in the development of ecological flow recommendations for North Carolina's Ecological Flow Advisory Board. Prior to her time at RTI, she worked at the Environmental Finance Center at the University of North Carolina, Chapel Hill, serving as a GIS and Financial Analyst focused on modeling future potential water transfers in North Carolina and developing sustainable finance strategies for the Upper Neuse watershed.

She has a Ph.D. in geography from the University of North Carolina, Chapel Hill.


Martin Doyle

Professor in the Environmental Sciences and Policy Division

Martin Doyle is a Professor at Duke University focused on the science and policy of rivers and water in the US.  His work ranges from fluid mechanics and sediment transport to infrastructure finance and federal water policy. His first book, The Source (WW Norton, February, 2018), is a history of America’s rivers.  His second book, Streams of Revenue (MIT Press, 2021) is an analysis of ecosystem markets. In addition to his role as a professor, Doyle has had several stints in government: in 2015-2016, he moved to the Department of Interior, where he helped establish the Natural Resources Investment Center, an initiative of the Obama Administration to push forward private investment in water infrastructure, enable water marketing, and increase the use of markets and conservation banks for species conservation.  Prior to that, in 2009-2010, he was the inaugural Frederick J. Clarke Scholar at the US Army Corps of Engineers.  

He has received a Guggenheim Fellowship, an Early Career Award from the National Science Foundation, recognized as a Kavli Fellow for the Frontiers of Science from the National Academy of Sciences and selected to deliver the Gilbert White Lecture by the National Academy of Sciences.

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