Mold and Legionella Lurk in Unused Buildings

If any parts of your church, school, camp, or college campuses have been unoccupied for over the past few months, you’ll want to review these preventive measures as you work to wipe out two microbial health hazards before you gather again.

Mold and Legionella (Legionnaires' Disease) are byproducts of excess moisture and a reduction in water use when buildings or parts of buildings sit empty for an extended amount of time. 


Mold can grow wherever there is moisture. Leaky pipes or roofs, even excess humidity, can lead to mold growth on hymnals, walls, ceilings, and more. It can be difficult to spot and is easily spread if you’re not careful. Mold is especially a concern for people with asthma and respiratory illnesses.

If your building hasn’t been fully occupied during the past few months, you’ll want to check some common culprits for mold.

  • Check your plumbing fixtures, roof, water heater, and HVAC drains for signs of leaks or mold.

  • Inspect and change your HVAC filters and make sure drain lines are clear to prevent water and mold issues.

  • If you’ve shut off your air conditioning to save money, change the filter and then turn it back on. It removes humidity from the air, a common cause of mold.

  • If your air conditioning has not been running for several weeks or months, consider having an HVAC professional turn it on the first time to check for any potential issues. It may also be wise to have a professional test and monitor your indoor air for mold, mildew, and other contaminants.

  • Clean air vent covers and ducts if they’re dirty. These also can be a potential source of mold growth if your HVAC has been idle for several months.

  • If your building has a basement, you may need to augment your air conditioning with a dehumidifier to help dry the air.


Legionnaires' Disease is a severe form of pneumonia. This lung disease is caused by the bacteria Legionella, which can be found in water that’s been stagnant in pipes, fixtures, and water heaters.*

Before regathering inside your building, consider the following simple steps as you seek to make sure your water is safe to use.*

  • Flush your water lines, especially staff drinking fountains (consider disabling drinking fountains in public spaces), faucets, and restroom fixtures. Simply turn them on and let them run for several minutes. You’ll also need to flush ice machines, which may require additional steps, such as dumping several rounds of ice.

  • Consider hiring a plumber to flush your water heaters, both tank and tankless. These appliances may require additional disinfecting before they can be used.

  • Make sure any indoor water features are properly chlorinated before running them.

For more information on Mold and Legionella, review this article from the CDC:

Additional Resource

*“Guidance for Reopening Buildings After Prolonged Shutdown or Reduced Operation.” Centers for Disease Control and Prevention, updated 7 May 2020.

Posted 7/14/2020

The information provided in this article is intended to be helpful, but it does not constitute legal advice and is not a substitute for the advice from a licensed attorney in your area. We strongly encourage you to regularly consult with a local attorney as part of your risk management program.