The author examines the effectiveness of some past and current products to help shower piping drain effectively to reduce Legionella growth.
by David Dexter, FNSPE, FASPE, CPD, CPI, LEED BD+C, PE
We learn more about Legionella bacteria almost daily. It has always been present in our water, but it’s effect was not recognized until an outbreak at the American Legion convention in 1976 in Philadelphia. Initially, the outbreak was not understood, but after much investigation, research, and study, the medical, scientific, and engineering communities have obtained a better understanding of the bacteria and continue to develop countermeasures to defend against future outbreaks of Legionnaires’ disease, as it has come to be called.
Legionella bacterium is a naturally occurring organism in water. There are more than 60 species of the bacteria, with Legionella pneumophila, serogroup 1, being the most prevalent type responsible for illness in humans. It is parasitic, making it difficult to eradicate within our potable water distribution systems. The best we can do as engineers and designers is manage risk through the control of biofilm development within those distribution systems. Potable water piping systems should be designed appropriately to avoid dead legs, maintain a minimum velocity, and control water temperature to retard the growth of, if not eradicate, the bacterium. Designing in such a manner may and probably will conflict with many codes, standards, and regulations. However, the main goal is always to protect public health, safety, and welfare, so we, as professionals, must balance the greater good against the constraints placed on the design.
To improve our designs, we need to rethink how this problem has been addressed.
Water distribution piping must minimize, to the greatest extent possible, any dead ends or uncirculated points within the piping network. In a typical bathroom group, for example, this will require the supply piping to first pass as close as practical to the least-used fixture (normally the shower), then to the next least-used fixture (the lavatory), and end with the most-used fixture (the water closet). By changing the piping layout to such a configuration, flow can be better assured with the least amount of dead or stagnant water, and if circulation is added to the cold water piping network, similar to circulating the hot water system, a minimum constant flow can be maintained to scour the piping walls and minimize biofilm growth.
While changing the piping configuration will certainly assist in managing risk, the shower faucet and shower arm/head or shower hose still pose an increased risk of exposure to Legionella. This risk is especially acute in healthcare applications, as the shower is used infrequently, if at all. How this risk might be better managed becomes something engineers and designers must consider.
Facility staff and water management professionals routinely recommend removing the showerhead and handheld shower hose to drain and sanitize them. This is a good beginning but leaves a relatively substantial amount of water and surface area with the potential for Legionella bacterium to grow, mainly in the piping from the shower faucet body to the point of discharge from the shower arm. This piping is concealed within the wall cavity, leaving no access or means to drain the stagnant/standing water. How can this risk be minimized or eliminated?
Almost every shower faucet is actually a tub and shower body with the tub opening plugged. How can we modify the design to accommodate the drainage of the shower riser, arm, head, and handheld hose? The plugged tub port can be used to drain the shower riser assembly and handheld hose. Making use of the tub port allows water to drain and air to enter, breaking any potential vacuum within the shower riser/handheld hose assembly.
Now the question becomes, how do we control the flow of water from the tub port?
Obviously, we do not want water flowing from that port during usage of the shower; it only needs to allow drainage upon completion of the shower with the faucet closed or turned off. This control will depend on the style of the faucet selected. Some faucets come with a diverter button built into the faucet body, and others rely on the diverter tub spout.
The faucet with the built-in diverter would be the easier selection in my judgment, as you already have a means to control flow between the shower and the drain (tub port) that is right in front of the user. The alternative (tub spout) would require a diverter valve or a ball drip-type inline check valve to control the flow to the drain. The problem with the diverter valve is that the user has to open and close it (it is not automatic), while the ball drip-type check valve relies on water pressure to close and a spring to open (no user interface).
The next consideration would be where to take the drain (tub port).
The drain (tub port) can’t interfere with the user’s use of the shower or cause water damage in the area. When I first began to research this, I thought about the spray head you might find in the old vitreous china cuspidors. (I know that most new engineers/designers have no idea what that fixture looked like, so I have provided an example in Figure 1 in stainless steel.) It was generally found in gymnasiums, next to the drinking fountain. However, this fixture has fallen out of favor because it was difficult to secure to the wall in a watertight manner, and the spray head is almost impossible to find these days. Thus, that idea was not going to work, primarily because a manufacturer could not be found.
Next I turned to representatives from the major fixture manufacturers. As this was not a product in their catalog, most were not interested in assisting in developing a solution that would enable a shower riser/handheld hose to drain. However, a Kohler factory representative in my area, Mr. Bill Berger, is a true professional asset. He and I discussed the problem and shared ideas back and forth to develop a workable concept.
In my judgment, the drain needs to be near the shower floor to minimize potential splatter. It also should not extend into the shower base to any great extent to avoid a trip hazard or injury to the user. The drain also needed to seal against the wall to prevent water intrusion into said wall.
As Bill and I discussed the idea, we remembered that several manufacturers offer a small spout, generally referred to as “toe tester.” (Bill was still willing to assist, even though his manufacturer did not have product to directly fit my needs.) Delta used to offer a forged brass toe tester spout, part number 060605A (see Figure 2). I say “used to offer,” as they have stopped producing it. Symmons manufactures a version (part number 071, see Figure 3), and Aquabrass also manufactures a toe tester (part number 15604, see Figure 4). However, both of those options extend a couple inches into the shower basin.
Bill came to the rescue with his continued research, as he discovered that Kohler offers a wall- or ceiling-mount bathtub filler (model number K-922, see Figure 5). This tub filler will work with any faucet—either integral diverter or utilizing an inline ball drip check valve. It protrudes less than 5/8 inches into the shower area and seals to the wall, when professionally installed.
This approach, for new construction or retrofit, eliminates the standing water in the shower riser assembly, thus reducing the risk of Legionella development in that region of the piping. To achieve appropriate drainage, the normally installed inline vacuum breaker should not be installed on the handheld shower. In doing what it is intended to do, the vacuum breaker would create a vacuum within the riser assembly and inhibit proper drainage. The vacuum breaker is not necessary, provided that the handheld shower is kept about 6 inches above the shower floor. As the shower riser assembly now has a clear path to drain and allows airflow, the risk of Legionella growth is greatly reduced.
In the time spent developing this concept, it was brought to my attention that Chicago Faucets is developing a specific faucet to market for this type of situation. Having reviewed the preliminary description of their prototype, I offer the following comments/concerns:
- The “elbow and valve drain for drainage above the valve” is located at the faucet level. This allows for an increased risk of splashing in the shower area as well as streaking down the wall as it drains.
- The prototype indicates that an “air vent” would be installed at the shower arm connection. If the piping is open on both ends, gravity will allow drainage, so a vent should not be needed. Even if the handheld hose is allowed to be left in an up position, most of the water would be siphoned out to the drain. (However, the handheld shower/hose should always be left in a hanging position for the best drainage.)
- The prototype has a “bumper and horizontal hose drain to prevent backflow” indicated. I am not sure what this device accomplishes or know any details as to its construction. However, if it is to be classified as a backflow, it will need to be certified to a standard.
The Ultimate Goal
Regardless of the approach, getting the water out of the shower riser assembly needs to be accomplished, minimizing the risk of Legionella growth at a reasonable cost.
David Dexter, FNSPE, FASPE, CPD, CPI, LEED BD+C, PE, is a Registered Engineer, Certified Plumbing Inspector, and Certified Plans Examiner with more than 40 years of experience in the installation and design of plumbing systems. He specializes in plumbing, fire protection, and HVAC design as well as forensics related to mechanical system failures. Dave serves as Chair of ASPE’s Main Design Standards Committee, Chair of the Bylaws Committee, and Co-Chair of the Professional Engineer Working Group. He also was the 2010–2011 President of the Ohio Society of Professional Engineers.
The opinions expressed in this article are those of the author and not the American Society of Plumbing Engineers.