Microorganisms in Plumbing Systems

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Certain plumbing design choices and building contractor practices can promote the growth of microorganisms in new plumbing systems. This can lead to corrosion of metals, increased metals concentration in the drinking water, holes in pipe walls, and waterborne illnesses. Basic steps can prevent the problem from occurring in the first place.

The story is repeated over and over. Occupants of a new building notice either discolored water coming from the water faucets or a “rotten egg” odor coming from the hot water.

Typically, what will happen next is that the plumbing contractor, realizing that corrosion is occurring, will pull the sacrificial anode rod from the hot water storage tank. The rod in a hot water storage tank is there to slowly corrode over many years, with the rod’s metallic properties diverting the flow of electrons to sacrifice itself to corrosion and protect the storage tank. But, in these cases, the anode rod has greatly corroded over a few weeks or months. The plumbing contractor will replace the rod, only to see the new rod corrode quickly again.

What most people don’t know is that the problem is of microbiological origin. Microorganisms are everywhere, and there are many different types of them. Some directly cause human illness and some do not. All waterborne microorganisms can grow into out-of-control populations when there are long periods of water stagnation or low flow and when disinfection chemicals are in inadequate concentrations. Under such conditions, microorganisms attach to plumbing system surfaces, both metal and non-metal. The microorganisms secrete an enzyme that forms a protective barrier around them, and they begin to multiply. This buildup of enzyme and microorganism colonies on surfaces is called a biofilm.

The biofilm is acidic and can create conditions at the pipe wall that allow metal to corrode. Metals that the plumbing sys- tem is made of, such as copper, iron, and even lead, have been found to corrode and their concentrations found to be increased in the drinking water when biofilms are present. Pinhole leaks in copper pipes have also been found. In addition, lower doses of chlorine and other disinfectants cannot reach the microorganisms protected in the biofilms. Once a biofilm is firmly in place in a plumbing system, it is very difficult, if not impossible, to remove. It cannot be flushed with high-velocity water because the required water flows and pressures cannot be achieved in plumbing systems. The biofilm cannot be removed by disinfection because many modern plumbing materials, and piping, cannot come in contact with the high concentrations of disinfection that are needed.


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