Addressing Stagnant Water in Buildings

As coronavirus continues to spread across the country, many facilities including college dorms, hotels, vacation condos, shopping malls, and other buildings are being shut down unexpectedly or operated with very low occupancy.  As a result, building water systems that normally have hundreds or thousands of gallons of water flowing through the fixtures, piping, and equipment daily may be stagnant for an unknown period of time, maybe several months. 

Stagnation can lead to serious problems that cause long-term damage, reduce property values, and be very difficult to mitigate once the building is reoccupied. What are the problems caused by water system stagnation, and what can building owners do to combat them?

Low flow and stagnation in water systems depletes disinfectant levels and stabilizes temperatures to ambient.  This provides ideal conditions for biofilms to form in hot and cold water storage tanks, hot water heaters, showerheads, faucets, ice machines, swimming pools, hot tubs, decorative fountains, and cooling tower systems.  Biofilms are communities of surface-attached bacteria that are directly linked to serious corrosion problems, biofouling, and the growth of Legionella and other premise plumbing pathogens. Once established, biofilms are difficult to remove from water systems even with high disinfectant levels.

Although each situation is different, there are practical steps you can take when shutting down a building to help reduce the potential for water system damage and waterborne pathogen growth:

• Keep the building HVAC systems live to maintain temperature and humidity control.
• If not required for HVAC system operation, the cooling tower, chillers, heat exchangers, and associated piping should be completely drained. Leaving the system filled with stagnant water can result in severe corrosion, biofouling problems, and contribute to the transmission of Legionnaire’s disease. 
• If the cooling tower is required for HVAC system operation, specific treatment protocols may be required to help address low load conditions.  Inhibitor requirements may need to be adjusted, and microbiological control can be more challenging. Do not discontinue water treatment if the tower is being operated.  
• Drain decorative fountains, hot tubs, and pools completely unless approved treatment and monitoring protocols are maintained. A Legionnaires’ disease outbreak in 2019 that resulted in over 140 cases and 3 deaths was linked to a poorly maintained hot tub display.
• Disconnect the water supply to ice machines, coffee makers, water filters, and similar devices.  Disinfect inlet lines and install new filters prior to start up. 
• Keep water heaters set at their designated temperature (ideally at or above 120⁰F).
• Flush all hot and cold water fixtures (showers, faucets, eyewash stations) at least weekly.  Document the flushing schedule with log sheets. Routine flushing may mitigate the necessity of disinfecting the potable water system before the building is reoccupied.
• Periodically monitor the chlorine level at the point of entry and locations throughout the building to ensure flushing provides adequate residuals. Simple test kits are available for chlorine testing.

If you have a Legionella Risk Management Plan, then many of these steps will already be defined. If you don’t, it’s recommended that you consult with a water treatment professional to advise you on specific measures you can take to reduce the potential for problems during shutdown and remedial steps to take prior to occupancy.