ASHRAE Journal - April 2020 - 66

COLUMN HVAC APPLICATIONS

Controlling Legionella

Legionella bacteria inhabit all types and varieties of
water sources, including lakes, streams and groundwater6 (Figure 1a). Other types of bacteria like E. coli are
also present in these same sources, as are viruses like
norovirus and rotavirus, as well as parasites like Giardia
Lamblia7. The public expects that water treatment plants
adequately combine ﬁltration and chemical treatment
to kill these and any other waterborne pathogens. This
trust, however, may be misplaced.
The Safe Drinking Water Act (SDWA) is the federal
law that governs water treatment to ensure it is safe for
human consumption. The National Primary Drinking
Water Regulations (NPDWR) are the standard for treating drinking water and are legally enforced by the EPA.
Yet, nationally, there's a concerning divergence between
theory and real accomplishment.
The EPA's NPDWR provides that 99.9% of the Giardia
parasite must be removed or inactivated from the
municipal supply. There is no stated limit, however,
for concentrations of Legionella. The expectation is that
the treatments to remove microbes like Giardia will also
result in the removal or inactivation of Legionella, but the
studies suggests otherwise.8 As the three studies demonstrate, the current municipal water treatment measures
are ineffective in neutralizing and inhibiting Legionella,
and instead allow various bacteria and other pathogens
to enter the distribution system and to pose health risks
to the public.
Also, the presence of Legionella without the presence of
other pathogens like Giardia demonstrates that although
treatment is effective for one pathogen, it does not eliminate Legionella, as assumed in the EPA's National Primary
Drinking Water Regulations.

Recommendations

The key takeaway is that it is imperative that the
National Primary Drinking Water Regulations be revised
to require testing for Legionella bacteria and also require
remedial actions as needed. Federal regulations must be
modiﬁed to ensure that Legionella bacteria is dealt with
at the water treatment plant and through the water distribution system, rather than making it the sole responsibility of the downstream users to remove and limit
the growth of Legionella bacteria. These measures would
then complement targeted downstream efforts to curb
Legionella growth, such as ensuring that disinfectants

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are at proper levels when the water is entering the
buildings.
There are new statewide efforts that represent good
examples of how this could work in practice. For example, Illinois recently modiﬁed their EPA regulations
to include raising residual chlorine levels to ensure a
continuing antimicrobial effort as the water makes its
way through the system. The same regulations require
water turnover in storage tanks to address stagnation,
and the elimination of dead ends in water distribution
systems. Louisiana and Pennsylvania have passed similar measures, and New Jersey is considering joining
this group. These efforts must be supplemented with
effective measures at the municipal water treatment
facilities to remove Legionella further upstream, closer
to the source.
All the studies mentioned in this column support the
fact that Legionella bacteria are widespread, and if not
controlled will result in greater numbers of Legionellarelated cases and outbreaks. Therefore, a focus on
efforts to better control pathogens in the public water
supply upstream by strengthening EPA requirements is
the rational approach to addressing the increased threat
of waterborne pathogenic bacteria-related disease cases
in the future.

References

1. Lu, J, Struewing I, Yelton S, Ashbolt N. 2015. "Molecular survey
of occurrence and quantity of Legionella spp., Mycobacterium spp.,
Pseudomonas aeruginosa and amoeba hosts in municipal drinking
water storage tank sediments." Journal of Applied Microbiology
119(1):278-88.
2. Donohue, M., et al. 2014. "Widespread molecular detection of
Legionella pneumophila serogroup 1 in cold water taps across the
United States." Environmental Science and Technology 48(6):3145 - 3152.
3. Llewellyn, A., et al. 2017. "Distribution of Legionella and
bacterial community composition among regionally diverse US
cooling towers." PLOS.
4. Hilborn, E.D., et al. 2013. "Surveillance for waterborne
disease outbreaks associated with drinking water and other
nonrecreational water-United States, 2009−2010." Morbidity and
Mortality Weekly Report 62(35):714 - 720.
5. Hlavsa, M.C., et al. 2014. "Recreational water-associated
disease outbreaks-United States, 2009−2010." Morbidity and Mortality
Weekly Report 63(1):6−10.
6. U.S. EPA. 2000. "Legionella: Drinking Water Fact Sheet." Ofﬁce
of Water. U.S. Environmental Protection Agency.
7. U.S. EPA. 2000. "Giardia: Drinking Water
Fact Sheet." Ofﬁce of Water. U.S. Environmental
Protection Agency.
8. U.S. EPA. 2009. "National Primary
Drinking Water Standards," EPA 816-F-09-004. https://bit.ly/2T2iToK
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U.S. Environmental Protection Agency.

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ASHRAE Journal - April 2020

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