Ten Ways to Minimize Stagnation in Water Systems
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Transcript of Ten Ways to Minimize Stagnation in Water Systems
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Figure 2. Both
regulator lines (A and
B) should be kept
open, or flushed
before use. The
domestic watersystem is exposed to
stagnant water in
the bypass line (C)
because of the dead
segments between
valve D and the tees
at E and F. Also, the
line cannot be
flushed to waste
without adding adrain and another
valve.
Figure 1. Piping left
after hot water
tanks were removed.
Ten Ways to Minimize Stagnation in Domestic Water Systemsby Matthew R. Freije
Posted: May 1, 2006
Piping with low or infrequent flows can be a breeding groundfor Legionella bacteria, but the following measures will help
to prevent these dead legs in water system designs.
Minimizing dead legs in domestic water plumbing is perhapsthe most widely recommended Legionella preventive measure, yet the advice isusually given without even defining dead legs, let alone substantiating the costversus benefits of removing them. Moreover, dead legscommonly thought of aspiping with low or infrequent floware only one of many causes of stagnation indomestic water systems.
Hospitals, nursing homes, hotels, office buildings and otherlarge facilities should have an expert evaluate the buildingwater systems and provide specific recommendations forminimizing stagnation. For now, though, implementing thefollowing measures will provide a good start:
1. Remove dead-legs. Although Legionella bacteria in deadlegs can contaminate an entire domestic water system, thepresence of dead legs does not necessarily mean there willbe a Legionella problem, nor will removing them necessarily
solve one. Before removing a dead leg, consider the benefitsversus the cost. Some dead legs present a greater risk thando others. Some are expensive to correct; others are not.The following rules are good practice:
a. Remove accessible dead legs. In equipment rooms andother areas where dead legs are accessible, the cost ofremoval will typically be minimal, so remove them. Forexample, if water heaters are abandoned, remove all thepiping associated with the installation to the point of flow,rather than simply capping the lines (see Figure 1).
b. Establish a policy of removing dead legs during plumbingrenovations. This should be added to any project specifications.
c. I f a dead leg cannot be removed without tearing out a wall, then leave it inthe wall but cut and cap it where it tees into the main. For example, if a sink isremoved, cut and cap the water lines serving the sink where they tee into themain, rather than at the wall.
d. If a dead leg is not accessible, and it cannot be cut at the main, then tryother methods of controlling Legionella bacteria before going to the expense of
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Figure 3. Design A
exposes the
domestic water
system to stagnant
water between the
tees and the bypassvalves, but design B
does not. Also,
design B allows the
bypass to be flushed
to waste by opening
the upstream valve,
closing the
downstream valve,
and opening the
drain. Flushing the
bypass before use is
tearing out walls to remove dead legs. The cost of removing dead legs that arebehind walls may not be justified without knowing if you have a Legionellaproblem, and that removal of the dead legs will solve the problem. (It probablywont.) If water tests indicate that Legionella bacteria are under control in yourfacility, then the expense of removing inaccessible dead legs is probably notwarranted. IfLegionella bacteria is not under control, then continuousdisinfection (e.g., copper-silver ionization or chlorine dioxide) will likely be morepractical and effective than tearing out walls and removing dead legs (see e.).
Building operators that do not periodically test domestic water for Legionella willneed to be more aggressive in correcting dead legs.
e. I f a continuous disinfection system is installed and operating properly, yettest results indicate that Legionella bacteria are still not under control, thendead legs and other stagnant water conditions may have to be corrected unlessanother method (e.g., point-of-use submicron filters) can be implemented. Thisscenario is not uncommon. Removal of stagnant water piping is often necessaryto make a disinfection system effective. A disinfectant cannot kill pathogens inwater when there is no contact with the pathogens, such as in a dead leg.
f. Choose flushing over removal only as a last resort. In some situations, facilityoperators choose to periodically flush dead legs rather than removing them. Forexample, rather than removing dead piping that used to supply an abandonedshower, a hospital will attach hose connections and set a maintenance policy offlushing the piping every two weeks. Relying on the maintenance staff to flushthe lines is a risk. Also, Legionella bacteria will, theoretically, build up in thelines between flushes, posing a health risk. And facilities operators will not knowhow often to flush the lines unless they gather a significant amount of data.
2. Do not use showers for storage unless the unusedpiping is removed.
3. Keep backup lines open, or flush them before use. Forwater lines that split into two branches and then come backinto one (e.g., to have a backup), both branches shouldideally be kept open at all times (see Figure 2). If onebranch is valved off, it should be flushed thoroughly to thedrain before each use, so that none of the potentiallycontaminated water is distributed to the building. This mayrequire adding a valve and drain at the downstream end of
each branch.
4. Design bypass lines to minimize the domestic watersystems exposure to stagnant water, and flush beforeeach use. (See Figures 2 and 3.)
5. Use all pumps regularly, preferably everyday. If twopumps are installed on the domestic hot water return line,but only one is operating at a given time, they should ideallybe rotated so that neither is offline for more than 24 hours
see Fi ure 4 . The same rinci le a lies to cold water
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critical, especially
since bypass lines
may go years
without use,
harboring foul water
that can
contaminate an
entire domestic
water system.
Figure 4. Unless one
of these hot water
recirculation pumps
and its associated
piping is removed,
both should be
operated all the
time, or rotated
regularly.
booster pumps, alternating the lead pump accordingly.Stagnant water in idle pumps and the piping associated withthem can provide a habitat for Legionella and other bacteriathat can enter the system when the pumps are turned on.
6. Flush vacant buildings, floors and rooms regularly. If abuilding or wing is completely out of use, requiring no water,the water system serving it should ideally be valved off and
drained. On vacant floors with undrained systems, anemployee in generally good health should periodicallyat least twice a week, butpreferably dailyrun water at all outlets at full flow for 30 seconds and flush alltoilets. This applies also to infrequently used sinks, showers or toilets in roomsthat have been converted from patient to office or storage use (occupants ofthese rooms should be encouraged to operate the fixtures daily). Prior toassigning a hospital patient or hotel guest to a room that has been vacant forthree or more days, an employee in generally good health should run the coldand hot water at each faucet and shower at full flow for at least two minutes andflush the toilets. For new hospital construction, consider electronic mixing valvesfor faucets and showers, which were recently introduced by ArmstrongInternational Inc. After approximately 12 hours of inactivity, these valves willautomatically run the hot and cold water for a few seconds at a safetemperature.
7. Use backup water supplies regularly, or flush thembefore each use. Most hospitals have a backup watersupply from the city main to the building that may go severamonths or years without use. These lines can build up foulwater that will be distributed throughout the facility when
the line is used. If backup supply lines are not kept open,they should be flushed before each use, which may requireadding a valve and drain at the downstream end, just beforethe building.
8. Store water for no longer than 24 hours. If hot waterstorage tanks are used, or if tank-type water heaters areused in lieu of instantaneous heaters, then design andoperate the system so that water remains in the tanks for nolonger than 24 hours. The same is true for cold water
storage tanks, unless they are treated.
9. Use water heaters daily. Even semi-instantaneous water heaters holdenough water (about 20 gallons) to pose a problem (see Figure 5). If removingbackup water heaters is not a reasonable option, then they should be usedregularly, preferably daily. If they are not used, they should be drained andisolated from the rest of the system, and disinfected before use.
10. Eliminate or isolate crossover piping. Pipes connectingbuildings or systems, often used as a backup supply of hot
or cold water ma harbor sta nant water that makes control
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Figure 5. The heater
on the right serves
the lower floors of
the building, theheater on the left
serves the upper
floors, and the one in
the middle is a
backup. This
arrangement
presents two
problems. First, even
if the middle tank is
valved off, its piping
leaves dead legs that
expose the two
operating tanks to
stagnant water. Thedead legs are short,
but could still provide
a habitat for
bacteria. Second,
stagnant water in
the dead piping that
is isolated with the
middle heater, as
well as in the heater
itself (if it isnt
drained), will enter
and possibly
contaminate the
domestic watersystem when the
heater is put into
service. If the middle
tank is not removed,
it should be used full
time in conjunction
with one of the other
two, or else flushed
and disinfected priorto each use.
ofLegionella bacteria difficult. If the crossover piping cannotbe eliminated, it should be isolated from the rest of thesystem, and flushed before use.
Priortize remedial measures based on a building assessmentDeserving higher priority are measures that either reduce asignificant risk, or are relatively inexpensive and should thusbe implemented out of good sense. Classify measures as
lower priority if the risk reduction benefit is questionable andthe cost of implementation is relatively high.
Matthew R. Freije
Matt Freije is president of HC Information Resources Inc., Fallbrook, CA (www.hcinfo.com). He is the author
of the book Legionellae Control in Health Care Facilities: A Guide for Minimizing Risk and three new Legionella
management plans for hospitals, hotels and nursing homes. He is also the editor of Legionella Enews, an
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international newsletter that covers outbreaks and new technology. Freije conducts Legionella building
assessments, serves as an expert in litigation related to Legionnaires disease, recommends domestic water
disinfection strategies and teaches seminars. He can be reached at (760) 451-1050, or [email protected].