Ten Ways to Minimize Stagnation in Water Systems

8/3/2019 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

[email protected]

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].

Ten Ways to Minimize Stagnation in Water Systems

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