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Pathogens in the Water Supply

  • 1.  Pathogens in the Water Supply

    Posted 12-07-2018 02:09 PM

    Here is a question that was sent to EWRI staff.  Can anybody provide any insight into this situation?: 
    "Can someone explain or lead me to a source of scientific information that can explain why low water pressure allows pathogens to enter the supply piping as opposed to normal pressure, making it necessary to issue a boil water advisory?"

    Barbara Whitten A.M.ASCE
    Technical Manager

  • 2.  RE: Pathogens in the Water Supply

    Posted 12-08-2018 06:15 AM
    This is not a simple question.  If pressure is maintained consistently throughout, then intrusion is minimized.  However in the presence of pressure transients, intrusion becomes more likely.  LeChevallier and colleagues have studied this a lot - see some of the references from this link:

    With valves and other devices in a water distribution system, pressure transients (including short term dips to negative pressure) can occur --- as LeChevallier demonstrates.

    I never like to say that you can totally prevent/eliminate pathogens from any environment (philosophically, you can never "prove" zero).

    Charles Haas Ph.D., F.ASCE
    LD Betz Professor of Environ. Eng. & Department Head - Civil, Architectural and Environmental Eng.
    Drexel University
    Philadelphia PA
    (215) 895-2283

  • 3.  RE: Pathogens in the Water Supply

    Posted 12-08-2018 06:32 AM
    I haven't heard about these issue, but I'm interested in. 

    The water piping system for drinking water is normally sealed and proofed with 15bar (in Germany obligated). The main issues with pathogens are contaminations during installation works or long dwell times in pipes. I can imagine, that a low pressure in the system increases the dwell time of water in the system. But this is just a guess. I would exclude the issue that the pathogenes contaminate water through the sealings, if they dont leak.

    I found an article about pathogenes in drinking water, but unfortuneally it is in German. Maybe the automatic translator in the browser delivers useable results. It has a bunch of further literature references and some of them are in English. Maybe some of them are useable.

    https://www.aerzteblatt.de/archiv/2518/Mikroorganismen-im-Trinkwasser (main article)
    https://www.aerzteblatt.de/archiv/2518/Mikroorganismen-im-Trinkwasser#literatur (literature references)

    Steffen Krei S.E., M.ASCE
    Dipl. Ing. (FH)

  • 4.  RE: Pathogens in the Water Supply

    Posted 12-08-2018 07:24 AM

    How about this study?

    Fox S, Shepherd W, Collins R, Boxall J. Experimental Quantification of Contaminant Ingress into a Buried Leaking Pipe during Transient Events. Journal of Hydraulic Engineering. Vol. 142, Issue 1 (January) 2015

  • 5.  RE: Pathogens in the Water Supply

    Posted 12-08-2018 08:26 AM

    Typical target water pressure in a municipal water distribution system is around 45 psi, or around 104 ft. of static head. That's a useful conversion in order to understand that the elevation (and therefore static pressure) of the water system at any point will vary with topography.  Larger distribution systems often have multiple pressure zones to accomodate the topography. 

    So if the average pressure drops to say 20 psi in the water main due to a break a few blocks away, the bathroom plumbing on the top floor of a 6 story building adjacent to that pipe might actually experience a negative pressure, thus potentially introducing pathogens to water piping system.  At that point, whenever the flow stops (or reverses direction) the pathogens are free to migrate in the pipe in all directions, thus contaminating the system.


    Thomas Sprehe P.E., BCEE, M.ASCE
    Director of Innovation and Technology
    KCI Technologies Inc
    Sparks MD
    (410) 316-7979

  • 6.  RE: Pathogens in the Water Supply

    Posted 12-08-2018 10:11 AM
    Not sure if my reply by e-mail earlier was actually received by anyone, but since the question included an interest in a "source of scientific information" I did a search and found the following.

    Fox S, Shepherd W, Collins R, Boxall J. Experimental Quantification of Contaminant Ingress into a Buried Leaking Pipe during Transient Events. Journal of Hydraulic Engineering. Vol. 142, Issue 1 (January) 2015

    Terry Baxter, PhD, PE, M.ASCE
    Professor of Environmental Engineering
    Northern Arizona University
    Flagstaff AZ
    Director, Applied Microbiology and Biotechnology Laboratory
    Part-time Professor Xi'an University of Science and Technology
    Standard Methods 24th Edition Joint Editorial Board
    Standard Methods Parts 1000 Coordinator
    ABET Senior Program Evaluator

  • 7.  RE: Pathogens in the Water Supply

    Posted 12-08-2018 09:22 AM
    Good morning,

    1.  All pipe networks leak.
    2.  As long as the pressure is maintained, the leakage is outward and the issue is economic.
    3.  When the pressure fails, the leakage can be inward and the issue is public health.

    Robert B. Finucane PE F,ASCE
    Edward Farrar Utiity District
    Waterbury, VT

  • 8.  RE: Pathogens in the Water Supply

    Posted 12-08-2018 10:48 AM

    Had a co-worker once that always said, "Better to leak out than in."

    A good paper specific to the issue, an EPA Study can be found at:
    Lots of other references listed at the end of this paper


    Michael Buechter P.E., D.WRE, M.ASCE
    Program Manager
    Metropolitan St. Louis Sewer District
    Webster Grvs MO
    (314) 968-9723

  • 9.  RE: Pathogens in the Water Supply

    Posted 12-08-2018 11:15 AM
    You may have a look at the paper below:

    Mohammad Solgi S.M.ASCE
    University of California, Santa Barbara (UCSB)
    Santa Barbara CA

  • 10.  RE: Pathogens in the Water Supply

    Posted 12-08-2018 11:29 AM
    The low water pressure may not be directly related to the problem, but is a facilitator.  Valve gaskets and pipe gaskets do an excellent job of preventing the water on the inside of the pipe from leaking outward; but they do not prevent water from the outside leaking in if the internal pressure ( hydraulic grade line) is less than the groundwater elevation outside of the pipe.  If there are any high points in the pipeline profile in combination with a low pressure and high flow demand (such as a fire flow to a hydrant or series of hydrants, it is possible that very low or even slightly sub-atmospheric pressures can exist in the pipeline (just like a siphon) and "invite" outside groundwater in through the gaskets or other pinhole pipe leaks.  It is possible there could be pathogens drawn into the pipe if they are in the groundwater or there is a leaking sewer or other source nearby.  I understand this was a concern in the recent fires in California.

    I saw this very clearly on a water treatment plant gravity filter with a pumped backwash supply pipeline wherein the pipeline was constructed with a high point above the filter water level.  When the backwash supply pump would turn off, water would gradually drain out of the pipeline through the valve gaskets undetected.  This created air pockets in the pipeline over time before the next backwash.  When the pumps would turn on for a backwash, the air would compress and be released into the underdrain in a sudden surge resulting blowing up the old style tile block underdrain.  Maybe the gaskets were old, but it happened.

    Joseph Reichenberger P.E., F.ASCE
    Professor of Civil Engineering
    Monterey Park CA

  • 11.  RE: Pathogens in the Water Supply

    Posted 12-08-2018 02:28 PM
    Low pressure in the network may allow contaminated water to be sucked into the pipes. This could happen, for instance, in a medical facility, where many bio hazardous materials are handled near faucets. So, instead of washing a contaminated material, hospital personnel would accidentally let pathogens be sucked into network pipes due to low pressure.And this could spread throughout the network.

    Mauricio Dziedzic Ph.D., P.Eng, M.ASCE
    Curitiba PR

  • 12.  RE: Pathogens in the Water Supply

    Posted 12-08-2018 09:26 PM
    The issue eluded to is that low pressure can cause a vacuum in part of the system, thereby drawing in contamination. This is why backflow preventers or vacuum breaks are required. A simple example is a homeowner is using a hose end sprayer. Elsewhere in the system, a fire breaks out in an old area of town and the fire department connects to an undersized main, which causes a pressure drop and a flow reversal at the homeowner's hose. Now the water supply just became contaminated with a herbicide. 

    Brian Rath P.E., M.ASCE
    Sr. Design Engineer
    Barker Lemar Engineering Consultants
    Grimes IA

  • 13.  RE: Pathogens in the Water Supply

    Posted 12-08-2018 09:17 PM
    Low pressure potentially allows water to infiltrate drinking water pipes from outside and that could be mixed with pathogens from leaking wastewater.

    High pressure insures any leaks in drinking water pipes are only out limiting exposure to pathogens outside.

    Sent from my iPhone

  • 14.  RE: Pathogens in the Water Supply

    Posted 12-08-2018 09:30 PM
    ​If the pressure drops low enough, the pressure outside the pipe may be higher, due to high groundwater, a puddle, a river crossing, etc. it is impossible to have absolutely no leakage in a water system, depending on the type of pipe, age, and other conditions there will be some points where low pressure can allow water, and pathogens, to enter the system.  If the pressure drops below atmospheric pressure air can enter.  Water system managers can never be certain the low pressure has not allowed water or airborne pathogens to enter the system if there has been a low pressure event, and therefore must err on the side of caution in issuing a warning until testing can be accomplished.

    William Forbes MASCE, PE, ME, BCEE
    Senior Principal Engineer/Vice President of Engineering
    Forensic Analysis & Engineering Corporation
    Virginia Beach, Virginia

  • 15.  RE: Pathogens in the Water Supply

    Posted 12-09-2018 02:58 PM
    EPA literature regarding revisions to the total coliform rule. Excerpt below

    Utilities commonly have a significant amount of leakage throughout the distribution system. In a
    survey conducted by Kirmeyer et al. (2001), 18 of 26 utilities surveyed had sufficient metering
    data to determine loss through leaks and breaks in terms of a percentage of total water produced.
    Seventeen utilities reported that less than 10% of total water produced is lost to leaks and breaks.
    One utility reported that water loss due to leaks and breaks is 18% of total water produced.
    Leakage points that are submerged may provide opportunities for intrusion of contaminated
    water during transient pressure events (Kirmeyer, et. al., 2001). Pressure changes in the
    distribution system can result in hydraulic surges that create low or negative pressure waves,
    which often go undetected by water system operators. As a low or negative pressure wave
    passes through a pipe, it can cause untreated, exogenous water to be drawn into the pipe through
    points of leakage or cross-connections. Sources of these pressure changes can be the effects of
    routine distribution system operation, such as pump startup and shutdown, opening and closing
    fire hydrants, and sudden changes in water demand (Kirmeyer et al., 2001). Further detail
    regarding the introduction of contaminants through intrusion is provided in the Distribution
    System White Paper The Potential for Health Risks from Intrusion of Contaminants into the
    Distribution System from Pressure Transients (LeChevallier et al., 2002).

    Justin Mahon P.E., M.ASCE
    Oradell NJ
    (201) 967-8177

  • 16.  RE: Pathogens in the Water Supply

    Posted 10-07-2019 08:50 AM
    Google "backflow prevention and cross connections" numerous sources and examples.

    James Mackie A.M.ASCE
    director of operations and maintenance
    Waretown NJ