Why the Sanitary Revolution Ended with Clean Water

John Snow is considered the father of modern epidemiology. In 1854, he demonstrated that cholera was associated with contaminated water.¹ Through a mapping exercise he was able to show that households clustered around a water pump on London’s Broad Street were getting sicker, while households not exposed to the water from the pump were healthier. His observations challenged a commonly accepted theory that dirty air, rather than water, was causing cholera. Through this work, Snow helped improve the health of the community by influencing local officials to turn off the pump. He also helped shift thinking toward clean water strategies that would later help influence the sanitary revolution, which shifted attention toward waterborne pathogen transmission.

Public health professionals commemorate Snow as a pioneer of epidemiology who catalyzed broader systemic change by emphasizing the urgency of disinfecting and cleaning water sources to improve public health. Over time that movement led to many advances, including the rise of sewage treatment plants, filtration systems, and modern public health infrastructure that work together to ensure water safety. 

While cholera spread through contaminated water, advances in modern science have since shown that the pathogens responsible for many illnesses, including RSV, COVID-19, and tuberculosis, are transmitted through the air. Despite this, efforts to improve air quality have largely focused on outdoor air, primarily by reducing chemical pollutants through regulations like the Clean Air Act. Establishing comparable standards for airborne pathogens has proven more difficult, requiring clear causal evidence, well-defined interventions, and demonstrations of cost-effectiveness at scale. This leaves an open question: if systems have been built to address the complexities of cleaning water, why hasn’t clean air followed the same path?

Existing clean air technologies remain underutilized 

To date, clean air strategies that reduce pathogens in the air rely on a layered defense of technologies that remove, dilute, or filter air. In most modern buildings, these strategies come in the form of engineering controls like ventilation and filtration that help clean the air around us. Additionally, modern buildings are increasingly adding monitoring systems that track CO₂ levels, which serve as a proxy for ventilation rates. While CO₂ monitoring can indicate whether enough outdoor air is being supplied relative to occupancy, it does not directly measure pathogen concentration or filtration effectiveness and should be understood as one indicator among several rather than a standalone measure of air safety.^2,3 

Ventilation is the first layer of defense and is widely accepted as effective, and minimum ventilation requirements are already written into building codes.² It is the first thing any building should get right. However, relying on ventilation alone to achieve clean air targets for pathogen control is typically not practical or cost-effective. It often requires expensive upgrades to air handling units or ductwork to carry the increased airflow, as well as resulting in a significant increase in energy costs in most climates to condition outdoor air for occupant comfort. This is where filtration becomes critical.

Filtration (such as MERV-13 or HEPA) is the second layer of defense and is also widely accepted as effective, with an established market.^4,5 Filtration can be integrated into a building’s HVAC system or deployed as standalone portable air cleaners. In either form, a key advantage over ventilation alone is that filtration removes particles from the air without requiring additional outdoor air intake, reducing the energy costs associated with heating or cooling. Despite this advantage, filtration remains underutilized relative to its potential contribution to cleaner indoor air.

However, like ventilation, filtration has practical limits. In-duct filters are constrained by the HVAC system’s fan capacity and ductwork design; upgrading to higher-efficiency filters can restrict airflow if the system is not designed to accommodate the added resistance. Portable air cleaners, while flexible and easy to deploy, must move enough air to meaningfully reduce particle concentrations in a given room, and increasing fan speed often introduces noise that leads occupants to turn units down or off. Real-world performance of both approaches depends heavily on proper sizing, placement, regular filter replacement, and consistent use. When these conditions are not met, the gap between rated and actual performance can be significant.

Together, ventilation and filtration form the foundation of clean air. They dilute and physically remove airborne particles, reducing exposure to pathogens while also improving overall air quality. While these approaches are essential to get right and deliver benefits beyond pathogen control, airborne transmission risk can persist in the time it takes for all infectious particles to be removed or filtered. This points to a gap where additional layers of protection, such as direct inactivation of infectious particles, may be needed.

Airborne illnesses impose significant burdens in the U.S. and globally

Since the sanitary revolution ended over a century ago, the wide-scale adoption of newer and innovative clean air technologies has not advanced to include additional tools and technologies that can further improve air quality. Why is that? 

In the United States alone, the economic burden of illnesses stemming from airborne pathogens imposes significant and recurring costs. For example, seasonal influenza results in an estimated $11.2 billion in annual economic burden, driven largely by indirect costs such as school absenteeism, workforce disruptions, and reduced productivity across the economy.⁶ With RSV, there is an estimated $6.6 billion in annual economic burden among adults aged 60 and over, with hospitalizations of these individuals accounting for 94% of direct medical costs and placing concentrated strain on the healthcare system.⁷

Despite these costs, investments in clean air interventions are often modest by comparison. Upgrading filtration in a commercial building, for example, can cost as little as $0.25 per square foot, with ongoing energy costs of just one to two cents per square foot per year, while portable air cleaners for classrooms can often be deployed at a cost of a few hundred to a few thousand dollars. In practice, even relatively small investments can reduce illness-related absences and associated economic losses. While costs vary depending on building size and system design, the gap between the economic burden of airborne disease and the cost of mitigation remains substantial, highlighting a persistent imbalance in how clean air is prioritized relative to clean water.

Globally, illnesses stemming from airborne pathogens can have an even greater impact, with millions of people still grappling with the more than 7 million confirmed deaths from COVID-19, alongside ongoing threats from persistent diseases like tuberculosis, which results in over 1 million deaths per year.^8,9 

Other countries are beginning to treat clean air more like clean water by establishing air quality standards, monitoring requirements and accountability standards. For example, South Korea has implemented indoor air quality standards for pollutants such as particulate matter, CO₂, and formaldehyde, across public facilities, including schools and transportation hubs, supported by national legislation and enforcement mechanisms.¹⁰ In Canada, the province of Ontario has made significant investments to improve ventilation and air filtration in schools, including large-scale deployment of HEPA filter units and upgrades to HVAC systems.¹¹ While these efforts vary in scope and enforcement, they represent early steps toward treating clean air as a managed public health resource rather than an individual responsibility.

The invisible cost of failing to implement clean air interventions 

Unlike contaminated water, poor air quality is often hard to detect. People often cannot see or feel when the air is unsafe, making it difficult to perceive risk or take action. In contrast, dirty water often signals danger through smell or visible contamination.

Exposure to airborne pathogens is also inherently probabilistic. Not every shared space leads to illness, and the risk from any single interaction may appear low. As a result, people continue to go to work, school, and other shared environments as part of daily life, often without clear signals to change behavior. While individual exposures may seem insignificant, repeated interactions across many people can accumulate into meaningful transmission at the population level.

Even as clearer targets for indoor air quality begin to emerge, it remains difficult to translate them into practice. Guidance on how to meet these targets in a cost-effective way, and how to measure whether they are being achieved, is still limited. While minimum ventilation standards are built into building codes, they are typically assessed during design and construction rather than continuously in operation. Without clear pathways for implementation and verification, consistent practices are difficult to sustain.

This implementation gap reflects a broader challenge in how clean air is managed. Unlike water systems, which are treated as shared infrastructure with defined ownership and accountability, clean air is often treated as a matter of individual responsibility or short-term mitigation. When responsibility is diffuse, accountability weakens, and consistent action becomes harder to sustain. Without clear federal standards and a clear understanding of whether interventions are working, efforts to improve air quality can remain fragmented, reactive, and uneven across settings, limiting their overall impact.

How Blueprint Biosecurity is advancing clean air technologies 

At Blueprint Biosecurity, program teams are working to close that gap by advancing countermeasures that build on the layered defense infrastructure in place today. Two promising approaches that have the potential to strengthen this framework are far-UVC and glycol vapors.

Far-UVC is a form of germicidal ultraviolet (UV) light that can inactivate airborne pathogens in indoor, occupied spaces.^12,13 Building on the demonstrated effectiveness of upper-room germicidal ultraviolet (GUV), far-UVC has the potential to serve as an additional layer of protection that can be used safely in occupied spaces, allowing for more continuous exposure compared to traditional GUV systems.^12,13 While ventilation and filtration are effective methods for improving air quality, incorporating far-UVC as part of a layered defense may provide additional protection, particularly in buildings where achieving clean air targets through ventilation and filtration alone is challenging. As evidence continues to evolve, far-UVC may help fill gaps in environments where existing approaches are difficult to scale or sustain.^12,13 

Glycol vapors, including propylene glycol (PG), dipropylene glycol (DPG), and triethylene glycol (TEG), are compounds commonly used in consumer and industrial products. There is both historical and emerging evidence suggesting that these glycol vapors, particularly PG and TEG, can inactivate airborne pathogens under controlled conditions, while related compounds such as DPG may offer similar potential but remain less well characterized.^14-16 As research continues, these compounds may offer a low-cost, widely available option for inactivating airborne pathogens in indoor spaces, particularly in emergency scenarios.

Across both approaches, research efforts focus on evaluating real-world performance, closing key evidence gaps, and identifying practical use cases, with an emphasis on safety, effectiveness, and viability in indoor spaces. Program teams are identifying key gaps in these emerging technologies that, if addressed, could unlock new tools to further strengthen the layered defense approach. In doing so, these efforts echo an earlier shift in public health, when new evidence challenged prevailing assumptions and laid the foundation for modern clean water systems.

Citations

1. Banerjee MR. The lesson of John Snow and the Broad Street pump. AMA J Ethics. 2009;11(6). Accessed April 1, 2026. https://journalofethics.ama-assn.org/article/lesson-john-snow-and-broad-street-pump/2009-06
2. ASHRAE. ANSI/ASHRAE Standard 62.1-2022: Ventilation for Acceptable Indoor Air Quality. ASHRAE; 2022.
3. ASHRAE. Indoor carbon dioxide (CO2) position document. ASHRAE; 2022.
4. U.S. Environmental Protection Agency. Air cleaners and air filters in the home. Updated 2023. Accessed April 1, 2026. https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home
5. Centers for Disease Control and Prevention. Ventilation in buildings. Updated 2023. Accessed April 1, 2026. https://www.cdc.gov/ventilation/index.html
6. Putri WCWS, Muscatello DJ, Stockwell MS, Newall AT. Economic burden of seasonal influenza in the United States. Vaccine. 2018;36(27):3960-3966. doi:10.1016/j.vaccine.2018.05.057 
7. Carrico J, Hicks KA, Wilson E, Panozzo CA, Ghaswalla P. The Annual Economic Burden of Respiratory Syncytial Virus in Adults in the United States. J Infect Dis. 2024;230(2):e342-e352. doi:10.1093/infdis/jiad559
8. World Health Organization. WHO Coronavirus (COVID-19) Dashboard. Accessed April 1, 2026. https://data.who.int/dashboards/covid19/deaths?n=c
9. World Health Organization. Global Tuberculosis Report 2025. WHO; 2025. https://www.who.int/publications/i/item/9789240116924
10. Ministry of Environment, Republic of Korea. Indoor Air Quality Control Act. Updated 2023. Accessed April 1, 2026. https://elaw.klri.re.kr/eng_mobile/viewer.do?hseq=63632&key=39&type=part
11. Government of Ontario. Ontario further improving school ventilation. Published 2021. Accessed April 3, 2026. https://news.ontario.ca/en/release/1000652/ontario
12.  Buonanno M, Welch D, Shuryak I, Brenner DJ. Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses. Sci Rep. 2020;10:10285. doi:10.1038/s41598-020-67211-2
13. Welch D, Buonanno M, Grilj V, et al. Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases. Sci Rep. 2018;8:2752. doi:10.1038/s41598-018-21058-w
14. Puck TT. The mechanism of aerial disinfection by glycols and other chemical agents. J Exp Med. 1947;85(6):729-739. doi:10.1084/jem.85.6.729
15. Ratliff KM, Oudejans L, Archer J, et al. Impact of test methodology on the efficacy of triethylene glycol (Grignard Pure) against bacteriophage MS2. Aerosol Sci Technol. 2023;57(12):1178-1185. doi:10.1080/02786826.2023.2262004
16. Gomez O, et al. Airborne murine coronavirus response to low levels of hypochlorous acid, hydrogen peroxide and glycol vapors. Aerosol Sci. Technol. 56, 1047–1057 (2022).