By Brooke K. Mayer, PhD, PE
A classically titled chapter in Robert Glennon’s book Unquenchable¹ poses the question, “Shall we drink pee?” The majority response is typically no, although it depends on who is asked the question and in what context. Globally, public support for indirect potable reuse, or IPR (when treated wastewater is used to augment drinking-water supplies after passing through an environmental buffer), is estimated at approximately 40 percent.² The dominant perspective shifts to stronger IPR support (80 percent) when there simply is no other option.²
Mayer et al. (2016)³ demonstrated that rates of national water reuse correlate significantly to water risk (e.g., water quantity and quality indicators, as well as regulatory indicators), whereas no correlation was found between rates of water reuse and wealth (i.e., gross national income per capita), human development index, or education. In other words, lack of other options drives water reuse such that desperation overrides the yuck factor. As one might expect, installations of treatment systems designed for alternative source waters, such water reuse and desalination, flourish in the wake of extended droughts. Unfortunately, our ambitions are largely fickle in that when the drought ends, apathy toward water sustainability and resiliency sets in (see Figure 1).
Figure 1. The hydro-illogical cycle. © National Drought Mitigation Center.
There are approximately 1,386 million Gm³ of water on Earth (a gigameter is one billion meters), and the law of conservation of mass tells us that this is all the water there ever was or ever will be. As such, one could argue that all the world’s water is reused.
More conservatively, Turner et al. (2021)⁵ reported that 80 percent of U.S. cities using surface water draw from supplies that are exposed to treated wastewater, with a range of 0 to 15 percent of cities’ total supply sourced from de facto wastewater reuse (i.e., unplanned reuse when a wastewater system discharges treated effluent into a water body upstream of a drinking-water facility). The situation is exacerbated under low streamflow conditions, wherein 40 percent of sites increased to at least half of the source water being from de facto reuse.⁶
Given that most regions on Earth experienced below-average streamflow and terrestrial storage water capacities in 2021 compared to the previous 30 years,⁷ de facto reuse may increasingly be the norm. Planned potable reuse can help satisfy water demands, as it involves higher levels of treatment compared to de facto reuse.²
Figure 2. Trends in U.S. population, total water use (measured as withdrawals, excluding those for thermoelectric power use, which is predominantly nonconsumptive), and per capita water use. Data is from the U.S. Geological Survey and the United Nations, as reported by Macrotrends.
Figure 2 shows that while the U.S. population has steadily increased, total water use remained relatively stable from about 1975 through 2000, with a notable decline since 2000. Translated into per capita water-use metrics, improved water efficiency and conservation facilitated a sharp decline in per capita water use beginning in the 1970s. With projected increases in population, continued increases in use efficiency plus development of new sources of water beyond those we have traditionally used are likely needed to enhance water resiliency.⁸ Alternative water sources can include rainwater or storm water runoff, desalinated seawater or brackish water, and recycled water from advanced water-reuse systems. Notably, the latter two options are climate-resilient.⁹ As such, water reuse is expected to continue to increase from current levels of approximately 7 percent reuse in the U.S.¹⁰ to upwards of 37 percent.¹¹ ⁸
IPR remains the most common type of water reuse. For example, WateReuse California indicated there were 36 permitted or planned IPR operations totaling over 933,000 acre-feet per year.¹⁴ The Texas 2022 state water plan projected that water reuse could produce more than one million acre-feet per year in the state by 2070, including roughly 67 percent IPR, 6 percent direct potable reuse, and 28 percent non-potable reuse.¹⁵
Further, arid western states are not the only ones climbing on the water reuse bandwagon; in Pennsylvania, the University Area Joint Authority recycles about 3 million gallons per day to ensure a sustainable supply, stabilize water rates, and decrease negative thermal impacts on aquatic life.⁹ In New York City, drivers for water reuse include housing affordability and incrementally avoiding retrofit costs for the existing combined sewer systems, thereby averting rate payer impacts.⁹
Although water reuse system costs generally exceed those of conventional treatment systems, cost avoidance of water/ wastewater system upgrades, water import, etc., can clearly support the economic case for water reuse in some scenarios. The unit operating cost of city-scale potable water-reuse systems ranges from 40 cents per cubic meter (Windhoek, Namibia) to $1.26 per cubic meter (Orange County Water District, CA),¹⁶ with typical values of 32 cents to 75 cents per cubic meter.¹⁷
For perspective, desalination costs are on the order of 50 cents to $1.80 per cubic meter,¹⁷ and the production costs for conventional drinking-water treatment range from roughly 25 cents to 45 cents per cubic meter, where the lower end of the range reflects economy of scale with larger capacity facilities having lower unit costs.¹⁸ For the Water Replenishment District in Southern California, the costs of importing water, for example, via canal network, were estimated to be 12 times higher than the costs of using tertiary recycled wastewater.⁹
To build on these drivers while avoiding the pitfall of the hydro-illogical cycle, more consistent efforts toward public outreach are needed to better convey the potential benefits of water reuse and further buoy progress in leveraging this substantially underutilized resource (and the only one that grows in step with population). For example, in 2021, the U.S. Bureau of Reclamation declared the first-ever official water shortage on the Colorado River,¹¹ triggering mandatory cuts in water delivery for areas of the Southwest.¹⁹ The associated drought contingency plans included water source diversification, such as water reuse, conservation efforts, underground water storage, and reductions in agriculture irrigation.¹⁹ These measures captured widespread public attention in the forms of awareness, concern, and possibly panic stages of the hydro-illogical cycle. However, winter 2023 brought near-record snowpack to California, alleviating some of the urgency of the drought response measures. Moving forward, we will see how this impacts longer-term efforts and if water reuse is negatively affected by the hydro-illogical cycle.
Even after the epic winter of 2023 alleviated some of the exigency for developing alternative water supplies, lean times are sure to return, and it is essential to plan ahead to establish appropriate source waters and treatment systems to help weather the dry periods. For public authorities considering enhancing long-term water resiliency by implementing IPR, Furlong et al. (2019) laid out a series of recommendations, as shown in Figure 3. Whether in times of drought or plenty, the water community can help to overcome the inertia of the hydro-illogical cycle by sharing the long-term water sustainability and security message widely: Water is too scarce a resource to cavalierly dispose of without recovering the valuable resources to the extent we are able.¹
Figure 3. Recommendations for public authorities considering implementation of IPR, as proposed by Furlong et al. (2019)
References
1. Glennon R. Unquenchable. Island Press, New York, NY; 2009.
2. Furlong C, Jegatheesan J, Currell M, Iyer-Raniga U, Khan T, Ball A. Is the global public willing to drink recycled water? A review for researchers and practitioners. Util Policy. 2019; 56:53-61.
3. Mayer BK, Baker LA, Boyer TH, et al. Total value of phosphorus recovery. Environ Sci Technol. 2016;50:6606-6620. doi:10.1021/acs.est.6b01239
4. Clarke R, King J. The Water Atlas. The New Press; 2004.
5. Turner SWD, Rice JS, Nelson KD, et al. Comparison of potential drinking water source contamination across one hundred U.S. cities. Nat Commun. 2021;12(1):1-12. doi:10.1038/s41467-021-27509-9
6. Rice J, Westerhoff P. Spatial and temporal variation in de facto wastewater reuse in drinking water systems across the U.S.A. Environ Sci Technol. 2015;49(2):982-989. doi:10.1021/es5048057
7. World Meteorological Organization. State of Global Water Resources 2021. 2022.
8. National Research Council. Water Reuse: Potential for Expanding the Nation’s Water Supply through Reuse of Municipal Wastewater. National Academies Press; 2012. doi:10.17226/ 13303
9. WateReuse Association. Access to Safe & Affordable Water: The Case for Investment in Water Reuse – the Once and Future Solution. https://watereuse.org/wp-content/uploads/2021/10/ Policy-Brief-Affordability.pdf
10. Rauch-Williams T, Marshall M, Davis D. Baseline data to establish the current amount of resource recovery from WRRFs. In: Water Environment Federation. 2018. Available at https://www.wef.org/globalassets/as.
11. U.S. Environmental Protection Agency. 2012 Guidelines for Water Reuse. 2012.
12. U.S. Geological Survey. Water Use Data for USA. National Water Information System: Web Interface. Published 2023. Accessed April 27, 2023. https://waterdata.usgs.gov/nwis/water_use/
13. Macrotrends. US population 1950-2023. 2023. https://www.macrotrends.net/countries/USA/united-states/population
14. WateReuse California. Potable reuse map of California. Accessed April 27, 2023. https://watereuse.org/sections/ watereuse-california/potable-reuse-map-of-california/
15. Texas Water Development Board. Innovative Water Technologies: Water Reuse.; 2022. https://www.twdb.texas.gov/publications/shells/WaterReuse.pdf
16. Guo T, Englehardt J, Wu T. Review of cost versus scale: Water and wastewater treatment and reuse processes. Water Sci Technol. 2014;69(2):223-234. doi:10.2166/wst.2013.734
17. Awerbuch L, Trommsdorff C. From seawater to tap or from toilet to tap? Joint Desalination and Water Reuse is the future of sustainable water management. In International Water Association. 2016.
18.Plappally AK, Lienhard V JH. Costs for water supply, treatment, end-use and reclamation. Desalin Water Treat. 2013;51(1-3):200- 232. doi:10.1080/19443994.2012.708996
19. U.S. Bureau of Reclamation. Reclamation announces 2022 operating conditions for Lake Powell and Lake Mead. https://www.usbr.gov/newsroom/#/news-release/3950
About the Author
Dr. Brooke K. Mayer is an associate professor in the Department of Civil, Construction and Environmental Engineering as part of the Opus College of Engineering at Marquette University. She holds bachelors, masters and doctorate degrees in civil engineering with an emphasis in environmental engineering from Arizona State University. She is a registered Professional Engineer in the state of Arizona.