GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted
Green Building News

Water Risks Higher in Green Buildings, Report Finds

Water conservation measures increase the age of water in plumbing systems, leading to higher levels of bacteria

Water conservation measures in green buildings mean that water is retained longer in supply lines, increasing the risks of bacterial contamination, researchers said.

Image Credit: Eric Norris / Creative Commons license / Flickr

Researchers at Virginia Tech say that water conservation measures in green buildings can increase the length of time that water stands in plumbing systems, thereby increasing the risk that water will become contaminated with microbes, including the bacteria that causes Legionnaires’ disease.

A report in Chemistry World said that the study measured chlorine levels, temperature, and microbial content in the water supply in different types of green buildings, ranging from an office building to a net-zero energy home. It found that chlorine disinfectant in the water decayed as much as 144 times faster in green buildings because of increased water age.

Green buildings typically have low-flow showerheads and faucets and may have water storage features. As a result, water sits in pipes longer than it would in conventional buildings, “risking problems with corrosion, unappealing taste and microbial growth,” the magazine said.

“We are at the beginning of a green building revolution where new products and approaches to water and energy conservation are coming to the market much faster than we can critically evaluate their impact,” lead researcher William Rhoads said.

The study was published by Royal Society of Chemistry. (For access to the report, free registration is required.)

Three green buildings studied

The number of buildings sold as “green” has increased exponentially, the report says, with LEED-certified buildings increasing from fewer than 7,500 in 2010 to more than 75,000 in 2014. As much as 48% of all new non-residential construction was expected to be green by this year.

“High water age is inherent to some green plumbing designs, and it has the potential to negatively impact the chemical and microbiological quality of drinking water in building plumbing systems,” the authors said. “More work is needed to help achieve water conservation goals without compromising water quality or public health.”

Researchers defined green potable water systems as those achieving at least a 20% decrease in use over conventional (no conservation) construction.

High water age is known to affect corrosion, taste, and odor, and it also has “possible implications for opportunistic pathogens” including Legionella, non-tuberculosis mycobacteria, and other waterborne pathogens of high concern in the U.S. These “opportunistic pathogens in premise plumbing,” or OPPPs, are “integral members of potable water microbial communities” but have been studied only a few times before in green water systems.

Researchers looked at water systems in three types of green construction: a 10,000-square-foot LEED-Gold healthcare facility, a net-zero energy single-family home, and a net-zero energy office. Total water storage ranged from an 80-gallon water heater in the healthcare facility to a 3,000-gallon cistern in the net-zero energy office building. A conventional household with no green features also was included. In all cases, copper was the primary plumbing material/ (PEX was used in one system beyond the plumbing manifold.)

A sampling plan was developed for each of the buildings, designed to test water quality as the water came out of the taps.

Water age and microbial content varied

In each of the three green buildings, the survey found “extremely high water age” because of energy- and water-conservation features. In the building with the 3,000-gallon cistern, water age ranged from 2 to 6.7 months. Water consumption at the healthcare facility was 60 times lower than it would be in a typical commercial building; at the net-zero energy house, a solar water heater increased hot water storage and hot water age from less than 1 day to 2.7 days.

At all field sites, the report said, bacterial markers were higher in stagnant water samples than in flushed samples. In the conventional house, levels of Legionella and other bacteria “were below the quantification limit in stagnant samples and below the detection limit in flushed samples.” That was not the case with the net-zero energy house, where genetic markers were “frequently present” in hot and cold stagnant and flushed shower samples.

A key finding was the rapid decay of chlorine disinfectant residuals in green buildings, once a problem thought to occur only rarely.

“This study reveals cause for concern about the public health implications of green building water systems, particularly with respect to potential creation of conditions ideal for the proliferation of OPPPs,” the study said. “Given the rapid expansion of green building construction at a time when OPPPs are now the primary source of waterborne disease outbreaks, fundamental research is needed to guide green building science down a path that protects public health while also conserving water and energy.”


  1. DEnd2000 | | #1

    Sounds like thermal storage
    Sounds like thermal storage and potable water should be Separate. A loop through an unpressurized Storage tank with an Overflow alarm should be a Simple and inexpensive solution.

  2. Dana1 | | #2

    That's sometimes called a "reverse indirect" water heater.
    Tanks of hot water with heat exchanger coils containing the potable water that heat up the water as it is being drawn has been a standard product for decades:

    They're not exactly cheap- quite a bit more expensive than standalone HW heaters, more expensive than indirect fired tanks operating as a zone of the space heating boiler, and comparable in cost to on-demand tankless hot water heaters.

    But reverse-indirects are NOT the solution. Per this blog piece:

    "In the conventional house, levels of Legionella and other bacteria "were below the quantification limit in stagnant samples and below the detection limit in flushed samples." That was not the case with the net-zero energy house, where genetic markers were "frequently present" in hot and cold stagnant and flushed shower samples."

    If the bacteria are detectable even in the cold distribution plumbing, the methods of heating the hot water are moot.

    Storage at high temps can kill most bacteria, but that also doesn't fix the room-temp distribution plumbing problem.

  3. user-626934 | | #3

    Questionable headlines...
    "Water risks higher in green buildings..."?? How about something more accurate, such as "water quality risk higher in buildings with larger-than-normal volumes of stored water and low water use"? Results from a sample size of three that includes an atypical off-grid building and a house with a (relatively rare) solar thermal system should not be extrapolated to the entire universe of "green buildings".

    Is it a surprise that the small office building with a 3,000 gallon cistern had old water? Is it a surprise that the house with 160 gallons of hot water storage had old water? Is it a surprise that the LEED health-care facility with pipe sizes grossly mis-matched from flow rates had old water?

    Some of the "green" buildings that I and others work on should have LOWER than normal water age, despite the low-flow fixtures, because we focus (among other things) on getting the pipe sizes "right-sized" to the flow rates. It's a shame these weren't studied as well...

  4. GBA Editor
    Martin Holladay | | #4

    Response to John Semmelhack
    Headline writing is tricky, and the number of characters we can squeeze into a headline is limited.

    You raise some important points. While some green buildings may have smaller tubing diameters than conventional buildings -- resulting, perhaps, in "fresher" rather than "older" water -- we don't yet have the data to support your hypothesis. Moreover, that happy result, if indeed your hypothesis is eventually proved, would be accidental -- not a deliberate result of a plumbing design that was optimized for water freshness.

    The questions raised by this study are important ones. Researchers need to focus on this topic until we have better answers. No matter which headline we choose -- GBA's 44-character headline, or your proposed 89-character headline -- this story is worth a read.

  5. charlie_sullivan | | #5

    Interesting links, Dana. I suspect that a key part of the reason they are expensive is that they are rated for high pressure, unlike the unpressurized tank Donald suggests. As people increasingly want to take advantage of the inherently low cost of thermal energy storage, the need for moderately large low-cost insulated tanks will increase. A tank for a boiler is generally rated for something like 250 F and 150 psi. For many purposes, a 140 F rating is adequate and the pressure rating could be 20 psi, or even zero, as Donald suggests.

    But as Dana says, that's not really the solution to this problem--that's a different topic.

  6. user-626934 | | #6

    Response to Martin
    Here's my new "constrained" headline... "Report: Low-flow fixtures + storage increase water risk". 48 characters. ;-)

    I agree, the story is worth a read...I read it! I'll certainly admit that I hadn't thought much about water age and quality with respect to "green building practices" prior to reading the study. My criticism is that the GBA story should have been more critical of the limited nature of the study. A quick phone call from the researchers to Gary Klein, for instance, would have yielded an abundance of potential test sites where the researchers could have examined my hypothesis. The study looked at three sitting ducks waiting to be plucked. Practitioners would have been better served by a study that asked the follow-up question to "What qualities of plumbing design lead to higher water quality risk?"...and that is, "What qualities of plumbing design lead to lower water quality risk?" Instead of telling us what we shouldn't do, we need to know what we SHOULD do. Perhaps the researchers are working on that one...but I'd rather not wait another two years for the report.

  7. GBA Editor
    Martin Holladay | | #7

    Response to John Semmelhack
    Many green building authors (like Gary Klein, whose articles have been published on GBA, as well as other authors who have been published here) advise the use of small-diameter tubing for hot water lines. This approach reduces the wait time for people using a bathroom sink or a shower located far from a water heater.

    I have never read any green authority advise builders to use small-diameter tubing for cold water lines. If they have, I'd be curious if you could point me to such an article. If such an article exists, I wonder what the justification for the design recommendation is -- I can't imagine that anyone was prescient enough to recommend small tubing in order to keep bacteria counts low.

    So I'm not as sure as you are that there are many green buildings out there that have managed to avoid the problems discussed in this article.

  8. STEPHEN SHEEHY | | #8

    Wait a minute
    "Green buildings typically have low-flow showerheads and faucets and may have water storage features. As a result, water sits in pipes longer than it would in conventional buildings...."

    Maybe so, but this "study" doesn't support that proposition. Maybe chlorine dissipates in water that is stored for a long period, but does that mean it's dangerous? Should we empty all of our pipes when we return from a weekend away to avoid the risk of death? I guess we could just leave the lawn sprinklers on 24/7. Of course then I'd need to buy sprinklers.

    Can you even buy showerheads or toilets that aren't low flow? I live in a pretty green home and we don't have any "water storage features", other than the same water heater you'd find in a typical house. Are 50 gallon water heaters safer than 80 gallon ones? There is no reason to think my water is any older than that of my neighbors whose homes are less green. Of course all of us around here have wells, so we don't have any chlorine added.

    The article discusses a few, largely unrelated pieces of data. It uses four buildings that are not comparable to one another. How hard would it have been to find two identical houses and run water at different rates and then compare actual bacterial levels?

    The piece doesn't say how much water was used in the single "conventional" house compared with the single "green" house.

    The article implies that water sitting in pipes for some length of time is dangerous, but doesn't define "bacterial markers." Are such markers dangerous? Can I get sick by ingesting bacterial markers?

    This study is worse than useless, because it adds to the growing list of things we are supposed to be afraid of, without providing any useful evidence that fear is justified.

  9. DEnd2000 | | #9

    Response to Dana
    I agree that reverse-indirect systems probably aren't the answer for everyone but it seems to me for buildings with large amounts of water thermal storage with low usage rates it's a pretty simple system to reduce issues. Pipe sizes, recirculation systems, increased pipe insulation etc... are all likely steps that may need to be taken, as well as reduction in bacterial contamination on the supply side.

    I'm curious as well on how this might affect water supply on the community side of our built environment. Widespread reduction in water usage will reduce the amount of water flushing through the distribution system, it stands to reason that this may increase bacterial contamination in the distribution system.

  10. morganparis | | #10

    And wait just another minute ...
    If this is a serious issue why is not a concern in connection with vacation homes and other seasonally occupied buildings where 'water age' can be far greater than a couple of days?

  11. BobHr | | #11

    how does this bode for the
    how does this bode for the pex manifold systems with individual lines running to each faucet. It was seems a lot of the lines would hold water for a longer period of time.

  12. cussnu2 | | #12

    The fact that they measured
    The fact that they measured an increased risk in a green home due to lower water turnover DOES NOT MEAN there aren't also problems (worse) in Vacation Homes or Home Run Pex systems. The study stands on its own

  13. morganparis | | #13

    The study stands on its own
    indeed, but as it stands it seems to be little more than a hit piece on some amorphous idea of 'green building'. What about a larger sample size. What about controlling for factors other than 'water-saving features' among the samples. What about controlling for the lengths of plumbing runs, and occupancy issues, and pipe materials and diameters, and distribution layouts. Not much of a 'study'.

Log in or create an account to post a comment.



Recent Questions and Replies

  • |
  • |
  • |
  • |