By Christopher R. Lloyd, PhD

Recent testing confirms the presence of alarmingly high levels of bacteria within the premise piping of various buildings with low or no use during the recent pandemic. Most workers celebrated the end of the nationwide shutdown (that left buildings drastically underused or totally vacant); however, it seems that the warnings issued by ASHRAE, the CDC and US EPA about water systems in underused buildings are becoming a reality.

Recent testing conducted by our company confirms that buildings subjected to shutdowns or reduced utilization have shown a deterioration in their water quality when returning to pre-pandemic schedules. This decline in quality has been traced to stagnant water within the buildings. Although it seems extreme, numerous buildings have shown dangerously high bacterial contamination levels (>1,000,000 cfu/mL of slime molds and iron-related bacteria) within the premise piping.

Although certain bacteria are always present in municipal water, they are typically controlled by the residual chlorine in the city’s distribution system. In unused and under-used buildings, stagnant organic material and bacteria can rapidly exhaust residual chlorine and allow the growth of biofilm that could harbor pathogens. At this level of contamination, simply flushing the piping may not be sufficient and if not properly addressed, that contamination can threaten health and safety.

During the last week of July, at Water Quality Association’s Conference in Las Vegas, NV, random tests were conducted for residual chlorine at various locations. Samples obtained from smaller, street-front locations (near the municipal distribution system) all measured over 0.5 mg/L; samples taken from larger buildings had no detectable level of residual chlorine.

The absence of residual chlorine in premise piping may be a clear indication that those systems are not adequately disinfected. And, like that unfortunate canary in the coal mine that succumbs to the bad air…it gives one a chance to react and rectify the problem before it gets worse.

Last summer, in anticipation of re-opening the economy, US EPA and the CDC issued the following guidance for all properties affected by the shutdown:

“Building and business closures for weeks or months reduce water usage, potentially leading to stagnant water inside building plumbing. This water can become unsafe to drink or otherwise use for domestic or commercial purposes. For example, optimal growth conditions for undesirable pathogens, such as Legionella bacteria, can occur when hot water temperatures decrease and disinfectant residuals (e.g., chlorine) drop to low levels. Water chemistry changes may also increase corrosion and leaching of metals, including lead, and may cause the formation of disinfection by-products. Turning on the water for immediate use after it has been stagnant can pose a risk to public health if not properly managed. Additionally, turning on water after a prolonged period of non-use could disrupt pipe and plumbing scales to such an extent that microbial and chemical contaminants could be released into the water.”

In January, the CDC issued its Legionella Toolkit that is “designed to help people understand which buildings and devices need a Legionella water management program to reduce the risk for Legionnaires’ disease, the key elements of a water management program, and how to develop it.” This Toolkit can be found online at

A key component to the CDC Toolkit is the reference to the ASHRAE 12-2020 guideline, which is designed to help in reducing the risk of dangerous levels of bacterial growth in buildings:

“ Growth. Biofilms play an important role in Legionella growth. Biofilms are complex and dynamic microbial ecosystems that form on surfaces within the building water systems. Biofilms impair the effectiveness of physical and chemical control methods, such as maintaining hot-water temperatures and applying chemical disinfectants. Legionella bacteria are known to invade and replicate within protozoa that are associated with biofilms. While inside these protozoa, the Legionella bacteria are further shielded from disinfectants and temperature extremes. Key factors that contribute to Legionella growth include sediment, temperature, water age, and disinfectant residual.”

The biofilms described by this section are occurring at an alarming rate within our communities, even though recent testing of local water sources and distribution systems found that all municipal systems tested were operating with adequate and appropriate levels of disinfection. Buildings that may be especially vulnerable include hospitals, care centers, churches, schools, office buildings, or literally any building, anywhere, that had limited use during the shutdown. Cities and local water operators are following the national guidelines for maintaining antimicrobial levels of disinfectant in their distribution systems, but building owners and managers are generally not, and this is mostly due to a lack of knowledge that they are responsible for the quality of the water in their building (not the city or county).

Keep in mind that chlorine can be quickly consumed after only a few hours if the bacterial load is too high, or the water is allowed to sit unused in the plumbing. Think about that. It takes a relatively short time for the disinfectant in the water to disappear and many of this country’s buildings have gone unused for over a year due to pandemic shutdowns. The lack of residual chlorine in the building water has become a potentially serious issue. Water sitting in these buildings becomes stagnant and can allow bacteria to colonize within the premise plumbing. Also remember that most bacterial colonies can double numerically every 20 minutes. Once established, they are particularly difficult to eliminate or manage. These colonies themselves aren’t the real issue: it’s the opportunistic premise plumbing pathogens (OPPPs).

OPPPs can survive in low-nutrient, low-oxygen environments. Furthermore, OPPPs interact with protozoans (usually amoeba), enabling them to resist treatment and persist in the environment. OPPPs resist treatment by forming biofilms, in which microorganisms aggregate together to form complex structures attached to pipe walls. Cell-to-cell communication is involved in marshalling the natural defenses of all the bacteria and protozoans against disinfection and regulates cell attachment and detachment in biofilms. Unfortunately, pathogenic bacteria frequently become ensconced in these protective biofilms. When this happens the likelihood of this deadly bacteria getting into air conditioning systems, hot tubs, showers, aerosolized water from toilet flushing and other sources is increased exponentially. Breathing water vapor from these sources allows Legionella to enter someone’s lungs, it’s downhill from there.

While working to identify and fix bacterial problems, one company has found that in all cases of contamination, the residual chlorine level in the building was non-detectable, likely indicating high chlorine demand in the building’s plumbing. Testing for residual chlorine is simple and inexpensive. Knowing residual chlorine levels enables quick and easy prediction of where problems may occur and will help to confirm if treatment steps have been successful. The author strongly advises all property owners, managers and concerned parties to familiarize themselves with national guidelines and take immediate steps towards controlling bacterial biofilm levels in their buildings. Proactive testing along with smart treatment can avoid a potential disaster.

What are the opportunistic premise plumbing pathogens?
The most notable of the pathogens that are present in premise pluming is Legionella pneumophila. This pathogen was discovered after 200 people were made seriously ill (34 of whom died) while attending the American Legion meeting at the Bellevue-Stratford Hotel in Philadelphia, PA, in 1976. Investigations found that Legionella bacteria thrive in hot weather and in cooling systems, and that inhaled tiny droplets of water containing either planktonic (free swimming) or biofilm-containing Legionella are particularly dangerous to frail individuals. Thus, Legionella is considered one of the deadliest opportunistic pathogens and is particularly dangerous in hospitals and care centers.

It isn’t, however, always the most prevalent. Pseudomonas species, which are famous for producing factors that allow it to outcompete other environmental bacteria and resist disinfection, are often found in or near POU fixtures (faucets, drains and shower heads). Non-tuberculosis Mycobacteria species can cause both pulmonary and non-pulmonary infections. Like their cousin that causes tuberculosis, these bacteria result in nasty infections due to their ability to adapt cell morphology, allowing them to resist both treatment and disinfection.

More recently, examples of antimicrobial resistant microbes have been discovered as OPPPs and may represent a class of new and emerging especially problematic pathogens. The good news is that the majority of problems associated with OPPPs (and with the biofilms that allow their propagation and survival), can be addressed by the development of a water management plan that uses the detection of residual chlorine to ensure the health and safety of premise plumbing.

Information on Maintaining or Restoring Water Quality in Buildings with Low or No Use. July 2020. coronavirus/information-maintaining-or-restoring-water-quality-buildings-low-or no-use

Maintaining Or Restoring Water Quality In Buildings With Low Or No Use. May 2020.

Restoring Water Quality In Buildings For Reopening – Checklist. May 2020.

Opportunistic Pathogens In Premise Piping. October 2018.

Guidance for Reopening Buildings After Prolonged Shutdown
or Reduced Operation. September 2020.

Toolkit For Controlling Legionella In Common Sources Of Exposure.
January 2021.

ASHRAE Publishes Updated Legionella Guideline. May 29, 2020.

Guidance to Help Minimize the Risk of Legionellosis. ANSI/ASHRAE Standard 188-2018, Legionellosis: Risk Management for Building Water Systems

Measurement Science Research Needs For Premise Plumbing Systems. May 2020

About the author
Christopher R. Lloyd, PhD, is a founding partner of RETEGO Labs, LLC and currently serves as the Vice President of Technology. He was responsible for the technical design and development of RETEGO’s patented chemical tests and analyte detection instrumentation and methodologies. Lloyd is an experienced chemist and microbiologist who has developed novel analytical laboratory and field methods for clinical diagnostic, security, environmental and residential service industry applications. He holds several US and international patents for devices that detect and measure inorganic analytes in water critical for scale and corrosion, as well as microorganisms, proteins and DNA from environmental samples. Lloyd’s peer-reviewed publications include a variety of studies detailing the rapid detection of environmental bacteria from arctic to desert locations, as well as the quantitation and taxonomic identification of pathogens and toxins from food, water and clinical samples.


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