I recall learning about Mary Mallon, aka Typhoid Mary, back in my school days. Mary worked at the beginning of the 20th century as a cook for several wealthy New York families and was renowned for her culinary skills. Unfortunately, Mary was also an asymptomatic typhoid carrier who apparently did not always employ the most hygienic practices after using the bathroom. Health officials now surmise Mary spread the disease through the water she used in her cooking, leading to dozens of cases of typhoid fever and at least three confirmed deaths. The public health response to those outbreaks helped drive major reforms in water quality management, hygiene education, and disease surveillance that continue to shape how we prevent water borne illnesses today. Today, ASSE International is at the forefront of leading efforts aimed at preventing contamination of our potable water supply.
Water quality protection begins with a simple but critical principle — contaminants must be prevented from ever entering the potable water supply. Once contamination occurs, remediation becomes far more complex, costly, and risky. This is why ASSE has developed a suite of backflow prevention standards such as ASSE 1013, Reduced Pressure Principle Assemblies; ASSE 1015, Double Check Valve Assemblies; and ASSE 1024, Dual Check Valves, that define rigorous performance requirements for assemblies and devices designed to stop both backpressure and backsiphonage. These products serve as the last line of defense between potential sources of contamination and the drinking water system, and they are indispensable in buildings that contain:
- Chemical dispensers or irrigation systems
- Dead ends or capped branches
- Equipment connected to potable water
- Extreme pressure fluctuations
- Low-use fixtures
Each of these conditions increases the likelihood that water may reverse direction within the piping system. Dead ends and low-use piping are particularly problematic because they create stagnant water zones where disinfectant residuals can dissipate, temperatures may rise, and microbial growth, including opportunistic pathogens, can thrive. Although ASSE standards do not prescribe how plumbing systems be laid out, they help ensure that if stagnation does occur, any degraded or contaminated water can be prevented from migrating backward into the potable water supply. This protection becomes even more important in large or complex buildings, where unused piping can remain stagnant for weeks or months without detection.
The COVID-19 pandemic highlighted this vulnerability. Many commercial, educational, and institutional buildings sat idle for extended periods, allowing water to stagnate and create ideal conditions for the growth of Legionella and other biofilmassociated bacteria. Legionella thrives in warm, low-flow environments, making poorly maintained plumbing systems a potential source of disease outbreaks. Recognizing this risk, ASSE has taken a leadership role in Legionella prevention through several key standards.
One of these is ASSE 1070/ASME A112.1070/ CSA B125.70, Water Temperature Limiting Devices, which governs thermostatic mixing valves. These valves help maintain safe and consistent outlet temperatures while still allowing water heaters to operate at higher storage temperatures to suppress bacterial growth. Another critical standard is ASSE 12080, Professional Qualification Standard for Legionella Water Safety and Management Specialists, which establishes the minimum qualifications for professionals responsible for developing and implementing water management programs. Individuals certified under ASSE 12080 are trained to participate in risk assessments, sampling plans, and mitigation strategies aimed at controlling Legionella and other waterborne pathogens.
Together, these standards support a comprehensive and proactive approach to Legionella control. They help ensure that water temperatures remain within safe ranges, that scalding risks are minimized, and that qualified personnel oversee the ongoing management of building water systems. This integrated approach is essential because temperature control, system design, and operational oversight all play interconnected roles in preventing microbial amplification.
Filtration and treatment systems also contribute significantly to maintaining water quality, especially in buildings with aging infrastructure, variable source water quality, or specialized needs. ASSE standards help ensure that these devices operate safely and effectively. For example, ASSE 1023, Electrically Heated or Cooled Water Dispensers, requires that point-of-use dispensers deliver water that is sanitary and free from contamination introduced by the device itself. Similarly, ASSE 1087, Commercial and Food Service Water Treatment Equipment Utilizing Drinking Water, establishes performance requirements for filters, softeners, reverse osmosis units, ultraviolet disinfection systems, and ozone systems. These standards ensure that treatment devices not only improve water quality but also avoid inadvertently degrading it.
In facilities with sensitive populations such as hospitals, long-term care facilities, schools, and foodservice establishments, these protections are especially vital. ASSE’s standards collectively form a robust framework that supports safe water from the point of entry to the point of use, helping building owners, designers, and operators maintain high-quality potable water and reduce the risk of waterborne disease.
As for Mary Mallon, she was widely vilified in newspapers for decades and ultimately died Nov. 11, 1938, while in long‑term quarantine on New York’s North Brother Island. Her case was extraordinary for the era because it revealed something previously unknown — a person could carry and transmit a dangerous pathogen without ever showing symptoms. Mallon felt perfectly healthy, so she rejected the idea that she might be infecting others. Her experience demonstrates how stigma and fear can overshadow scientific understanding and undermine effective public‑health responses.
Fortunately, the combination of antibiotics, public education, vaccination programs, and the sanitation improvements championed by ASSE and other organizations has dramatically reduced the incidence and spread of typhoid fever in many parts of the world. However, the disease remains a persistent challenge in several endemic regions of Africa, Asia, and Latin America. For that reason, ASSE’s guiding principle of “Prevention Rather Than Cure” continues to hold significant relevance today.
