By Abigail Cantor, P.E., Chemical Engineer and Water Quality Specialist
I just finished investigating yet another brand new building with corroding copper pipes. Fixtures were stained green and the blonde residents had green stains in their hair! This situation is upsetting every time I see it. And, it seems to happen quite a lot — on both large commercial buildings and in private residences.
But, this problem can be prevented. This is why I wanted to raise awareness of the problem by writing a series of articles in Wisconsin Perspective in 2012 and then by bringing the articles together into a booklet called What’s Bugging Your Pipes: How Microorganisms Affect Plumbing Systems.
In short, microorganisms grow in water systems whenever water stagnates or resides too long in the pipes and tanks. They attach to surfaces with an acidic enzyme that can corrode metal. This situation is called microbiologically influenced corrosion or MIC. This can lead to increased metals concentration in the water with possible discoloration as well as pinhole leaks in metal pipe walls. In addition, with conditions good for microbiological growth, there is an increased risk of encouraging the growth of microorganisms that cause water-borne illnesses.
Excessive microbiological growth can occur anywhere in a water system beginning at the water source, in the water service line, in point-of-entry water treatment tanks, in the hot water system, in point-of-use water treatment devices and finally, in the faucets. The key is to identify volumes of slow-moving or stagnating water within a water system.
One location of slow-moving water in a plumbing system is in its on-site water treatment. The best practice is to provide on-site water treatment only when it is absolutely necessary. There are many possible contaminants in water but it must be determined which contaminants really pose a threat. Sizing the equipment so that it has a minimum volume and surface area to do the job required is very important. Finally, there needs to be an automatic clean-in-place system or manual cleaning protocol that can keep the equipment free of microbiological growth.
Proper plumbing design is also critical in preventing MIC. Many luxury plumbing features, such as multiple-head shower sprays and large bathtubs, increase the required water flow, and subsequently, the pipe size and hot water storage requirements. Customers must be made aware of the trade-offs in selecting some of these features. There are ways to use these luxury features with some restrictions and still enjoy them. The new reality is that a plumbing design should focus on minimizing volume of water and interior surface area in the complete plumbing system.
Another battlefront for MIC is to prevent microorganisms from entering the building’s plumbing in the first place. Private well owners need to understand the structural and hydrogeological issues of their wells. Municipal water utilities need to maintain disinfected water of low microbiological activity throughout the distribution system.
Disinfection, typically in the form of chlorine, is necessary in water to prevent excessive microbiological growth. Once microorganisms attach to the walls, then another type of chemical that can break down the protective “biofilms” around the microorganisms is needed in addition to disinfection.
Routine monitoring must be performed in the water to assure that microorganisms are under control. One parameter to track is the disinfection concentration in the water to determine if there is “ammunition” to keep up the fight against excessive growth. This can be done with a relatively simple test kit. A second parameter to track is a measurement of microbiological activity called ATP. This analysis can be performed at some water laboratories.
In summary, to prevent MIC from occurring, design the plumbing system with minimum volume and surface area to prevent microbiological growth. Then, maintain a clean plumbing system by cleaning any treatment equipment and tanks and keeping the water disinfected. Finally, monitor routinely to confirm that microbiological growth is low and the water is disinfected.
If MIC is already occurring, monitor to determine where the sources of microbiological growth are in the plumbing system. Make sure that there is adequate disinfection in the water and possibly use a chemical to destroy the protective biofilms around the microorganisms. Plumbing systems may have to be modified to lower the volume of water stored. Then, maintain a clean system and monitor to confirm that the problem does not re-occur.
The past articles and, now, the booklet on What’s Bugging Your Pipes was written for plumbing designers, building contractors, municipal water utility managers, and property owners to raise awareness of MIC and suggest ways to prevent and remediate the problem. The growth of microorganisms in water systems can be prevented with everyone’s participation.
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