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Mitigating Stagnant Water Diseases and Damage During the Pandemic

Posted by Jonathan Zinser

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For the better part of a year, “normal life” has taken a back seat. 

With the coronavirus pandemic forcing unprecedented public health protocols, many major public and private institutions, such as universities, have found themselves in a tough position: closed. As part of this shutdown, their major utility systems were turned off. 

While turning systems off is a cost-saving measure, it’s not without its risks.

For certain building systems -- such as HVAC and water -- sitting dormant for long periods of time greatly increases the chances for damaging stagnant water within them. Stagnant water conditions typically result in biofilm formation, which can harbor and grow dangerous waterborne pathogens, such as legionella. In turn, there’s a higher probability that standing water contains dangerous waterborne pathogens, such as legionella.   

Turning utility systems designed for continuous use off and turning them back on again isn’t something that should just happen. Preventing waterborne diseases from spreading throughout a building via utility systems requires some work long before occupants return.

What is Stagnant Water and How is it Problematic?

Often referred to as “standing water,” stagnant water is water that’s left sitting for long periods of time. 

With no movement and aeration, stagnant water becomes a prime breeding ground for biofilms, or a collection of bacteria or fungi. Left untreated, stagnant water often becomes home for dangerous diseases and pathogens such as:


  • Legionella
  • E. coli
  • Nontuberculous mycobacteria 
  • Pseudomonas-related pneumonia


Stagnant water also causes physical damage to a utility system, corroding metal pipes.

In older buildings, this is particularly worrisome as some pipes contain lead. For pipes supplying potable water, the presence of lead can be deadly. Metal corrosion in other systems, such as boilers, chillers, and cooling towers, compromises their ability to function properly. 

In HVAC systems, stagnant water poses a unique set of issues. Not only does corrosion potentially affect their ability to work, but deadly legionella in their water can also spread quickly once the system is turned on. 

Learn how Rochester Midland Corporation can help you avoid stagnant water issues:


5 Ways to Reduce Stagnant Water Diseases & Damages  

To reduce the possibility of long-term damage to your systems from stagnant water, the Centers for Disease Control and Prevention discourage turning them off indefinitely.  

Here are five steps you can take as a building engineer, property manager, or owner to keep your utility systems safe from stagnant water and legionella during periods of limited use: 

  1. Keep hot water hot and cold water cold -- this discourages microbial growth, which is mostly likely to occur in room-temperature water.
  2. HVAC cooling towers should be drained if not in use. This prevents corrosion, biofouling, and legionella bacteria proliferation.
  3. Boilers should be placed offline following a wet or dry lay-up procedure to prevent corrosion. Failing to do so could result in oxygen pitting, general corrosion and iron fouling, and ultimately increased energy costs and/or premature failure.
  4. Create and follow water management protocols that include testing for disinfectant levels and periodic flushes. 
  5. All chemical feeds need to be flow-interlocked to safeguard against chemicals being fed into “dead water,” as concentrated chemicals can corrode piping and equipment. Flow-interlocking also helps ensure that chemical is appropriately dosed or not dosed during all load conditions.

Safely Turning HVAC and Water Systems Back On 

With many public and private facilities anticipating a full reopening in the months ahead, getting utility systems back up and running is one of the first priorities. Turning these systems back online isn’t just a matter of flipping a switch. 

Preventing potential waterborne pathogens such as legionella from spreading through utility systems involves taking steps to thoroughly prepare for normal use. 

For HVAC systems, the CDC recommends: 


  1. Inspecting the system for apparent dampness or mold. If mold is detected -- typically by sight or smell -- contact a commercial cleaning service for system sanitation.
  2. Changing and replacing filters as needed
  3. Completing a flush-out by running the system for 48-72 hours with air dampers open before a building is reopened.
  4. After the flush-out, routinely inspecting the HVAC system
  5. If your university does not already have one, developing and implementing an HVAC maintenance plan


In plumbing systems -- which supply water to kitchen faucets, dorm showers, and drinking fountains -- the CDC advises you should:


  1. Inspect all elements of the system 
  2. Flush the water system at all points of use, e.g. showers, sinks, and faucets
  3. Clean all water fixtures
  4. Test water for the presence of lead or other heavy metals
  5. If you do not already have one, develop and implement a water system maintenance plan

Eliminating Stagnant Water Dangers for Public Safety 

While bringing utility systems back online to run at normal capacity signifies an encouraging step toward normalcy, it should be done with great caution. 

Preventative maintenance coupled with critical inspections and system flushes ensures your utilities not only work as they’re supposed to, but also preserve public safety.


Preparing for reopening?

RMC can help you make sure your HVAC and water systems are ready to run safely. Learn more about our services.


Topics: legionella, legionella risk minimization, Pandemic, Water Treatment, water management plan, HVAC, Stagnant, cooling


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