I agree with Bruce. If your water supply has not been compromised, there is little risk for legionella bacteria. There is typically enough chlorine residual in city water that will kill the bacteria. Where there is a greater risk is when the water is warm, open (hot tubs, cooling towers, etc.) and not disinfected.

At 122 F 90% of Legionella is killed in 80-124 minutes, but a heater that's been off, even for a week or more, is probably fine as long as the water supply is safe to drink.

Your concern is valid. This is coming from someone that went to the ER almost 2 years to the day because I wasn't feeling well. Needless to say, I had Legionnaires.

The County Health Department informed me it had not reported a confirmed case to the CDC for our county since 2002. I was surprised at the information they wanted from me. Of course the hospital reported it to the Health Department. Hot tubs, stagnant water of any kind, water sprayed on fresh veggies at a farm market, your own shower head or pipes, drains, and just about everywhere you find water is suspect for it. I believe I got it from mowing. I run a tractor all summer on x-ways and attempt to cut back into cat-tails and the high stuff along ditch lines. I think this is where I got it. Surprising, the Health Department, CDC, or no one else investigates unless more than one person is involved.

For me the Legionnaires was bad. But what came afterwards was worse. I got sepsis and that causes some serious issues and apparently can lead to death.

I do attempt to be cautious around stagnant water, but not to the point that I'm paranoid. And, I'm still mowing those x-ways.

I guess my point is to be aware, but not to the point of being paranoid.

roof35: Your situation sounds serious. However, I don't see how it applies to water heaters in closed plumbing systems that have not been contaminated - or that the risk increases because the water heater has been off for several days.

Jake. The Health Depatment claims you can get it from shower heads You can also get it from drains which contain stagnant water.

I'm not understanding your point The concern is real It has to do with other plumbing in the home

roof35 The question was (I'm paraphrasing here): "Does a home water heater being off for a period of time (a week, for example) significantly change the risks associated with contracting Legionnaire's Disease?" The answer is "No, probably not".

The risk of Legionnaire's Disease is very small to begin with (your county health department confirmed that - no reported cases since 2002). The likelihood of getting it from domestic plumbing that is closed and biologically safe to begin with (not contaminated by floodwaters) is much smaller.

My understanding is that you have to inhale water droplets that contain the bacteria - so normal drains containing stagnate water don't seem to be a huge threat.

Chlorine residual from municipal water supplies will kill the bacteria.

There are situations where the risks are elevated that have similar factors:

1. The water is warm, but under 122 F.

2. The water is made into a mist so that water droplets are inhaled

3. The water is stored in the open and not disinfected

Cooling towers and hot tubs that aren't maintained fit this. Your home shower - not so much.

I've said it before on here: We are really, really bad at understanding comparative risks. The risks associated with you operating a mower on a highway, or driving a car, or climbing a ladder, or smoking, or falling in the shower (you do have grab bars, don't you), vastly outweigh the risk of getting Legionnaire's Disease from your domestic plumbing.

If the home has a 1 way valve such as a pressure regulator, the system was sealed like a bottle of water. The real question in my mind would be the outside upline water supply, as it feeds down to the home.

Jake

I see you focused on the subject line, instead of the overall content of the body of the subject. I now know why you're dwelling on your take the risk is low.

I tend to address the over all body about the risk, not just the subject line. The risk increases for the shower and the drains when no water has been ran through them the longer they sit. If you read the entire context of the body, this concern was addressed.

The concern is real, no matter how rare it happens. Over all in the United States there is approx 20,000 confirmed cases per year. You are right about understanding the risks. As long as the concern is there, it should be acknowledged and not by an oh well, the risk is minimal.

I actually said I believe I got it from mowing. The Health Department pointed it out I could have gotten it from my own shower. I tend to believe them over you saying "not so much" to get it from your home shower. Their information comes from the CDC, not someone on the Houzz speculating what they think are the risks. To not be concerned, is just plain ignorant no matter how small the risk when there are 20,000 confirmed cases a year.

roof35: I'm terribly sorry you got sick.

I answered the question that was asked, and within the context it was asked and with background info on why this all is a very, very low risk issue in regards to home plumbing.

So by all means, "be concerned" whatever the hell that's supposed to mean. If you want to never take a shower again - feel free.

Do people get this disease?: Yes.

Are there significant risks from standard home plumbing?: No, not that have been clearly identified.

Are there increased risks based on what the OP asked?: No.

Are there actionable items to reduce the risk from home plumbing?: No, not that I am aware of. I've not seen any recommendations from the CDC to set water home heater temps to 140 F, for example.

There are recommendations for commercial and institutional plumbing systems that are beyond the scope of this blog.

Jake,

What is showing in the subject content on my monitor is that you didnt address it as whole subject. You may want to read it again.

You're totally missing the obvious about stagnant water and the OP's concern Either by choice or you are really missing it

i see you're upset because I point out the obvious about reading comprehension. I'm sorry I hurt your feelings. You can attack the messenger all you want. It doesn't change facts

There's a ton of information on the subject. You may want to check it out before making further comments like a know it all. It's a bit embarrassing isn't it?

Have a good day.

Intentional irony . . . or no?

Here's some information that could be helpful.

"The American Society of Sanitary Engineering recommends setting the temperature of home water heaters to 135 degrees to 140 degrees Fahrenheit, a range shown to destroy bacteria such as Legionella. At those temperatures, bacteria can neither thrive or survive to contaminate fixtures downstream from the heater. Adjusting a water heater to a higher temperature must always be accompanied by the installation of anti-scald devices in the home by a licensed plumber to prevent potential burn injuries, if such safeguards are not already present."

Here's a link to the article.

Here's a link to the source material and then scroll down to page 3.

Here's a link to the other source material for the article.

I've been living dangerously for 12 years. On a private well system, so no municipal treatment/chlorine added. Tankless water heater set at 102°F majority of the time. Raised occasionally on a temporary basis for washing laundry and the few bits of cookware/dishware that don't go in the dishwasher.

Our water sits in the ground for years to millennia, fully exposed to the environment, sits in the town water tanks for months, sits in pipes for days or weeks all without inducing an epidemic of Legionella pneumonia. I think (speaking as someone who has had a career in infectious disease) the primary risk comes from recirculating water or water continually condensing that gets atomized and inhaled, as in air conditioning systems. I'd worry much more about the hot tub with the bubbles than my hot water tank.

If sitting contained were an issue you'd see a lot of disease associated with the use of bottled water. I'm not aware of any such data.

If you're really concerned just flush the tank and then crank the temperature up to over 140 deg for a day, that will kill Legionella and most other bugs.

rwiegand : Exactly. There are situations to be concerned about with regards to this bacteria, but generally residential water systems aren't high on the list.

As for the American Society of Sanitary Engineering - that's interesting, but not a widely held position. What is more widely held (it's on virtually all water heater instructions) is not to run heaters that hot because of scalding.

If this is becomes code then it will have other implications (such as installing thermostatic mixing valves after the heater).

I set my water heater at 135 and that works fine for me. Here's some information that I read online that was interesting.

"* 70 to 80 °C (158 to 176 °F): Disinfection range
* At 66 °C (151 °F): Legionellae die within 2 minutes
* At 60 °C (140 °F): Legionellae die within 32 minutes
* At 55 °C (131 °F): Legionellae die within 5 to 6 hours
* Above 50 °C (122 °F): They can survive but do not multiply
* 35 to 46 °C (95 to 115 °F): Ideal growth range
* 20 to 50 °C (68 to 122 °F): Legionellae growth range
* Below 20 °C (68 °F): Legionellae can survive but are dormant"

If someone has small children or the elderly then scalding would be a concern. Here's a link to a scalding chart that shows the amount of time for scalding at various water temperatures.

Normally city water has treatment to impair growth. If concerned drain the water heater run a bit more water through and refill. Will only waste in gallons whatever size the heater is. Possibly need a new drain, you would find that at the hardware store in the water heater parts area. Often these drains get clogged with sediment, better to replace the drain before it gets clogged and full of water. Use teflon tape on threads and pipe wrench to remove/install.

Standard water heating setting is 120F. As posted above, no growth at that temp and it has less chance of scalding at the factory setting (uses less energy too).

I have my water heater at 150 and a mixing valve at 116. :)

There is growth at 120. No growth above 122.

Hey you are right, thanks for that info. For those that dont know, a mixing valve at the water heater brings in cold water to the hot as it is deployed to get rid of scald chances. I will probably look into doing this.

http://www.cashacme.com/resources/hot-water-safety/

The answer to preventing both Legionnaires disease and hot water scalding is to store distributable hot water at a high temperature and temper it to a safer temperature before distribution to the fixture.

http://homeguides.sfgate.com/turning-water-heater-up-kill-bacteria-54596.html