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Public Health Guidance for Ensuring Water Quality in Buildings with Prolonged Closure or Lower Usage


Water quality can be seriously compromised when it sits in building plumbing systems for extended periods of time without movement. As buildings close and reopen during the COVID-19 pandemic, it is important to keep in mind how prolonged periods of little to no water usage can negatively impact water quality, creating the potential for serious health concerns if proper flushing and reopening procedures are not followed.


Concerns That May Arise When Building Water Systems are Idle

  • Sediment build-up in pipes, leading to mechanical issues and bacterial growth.
  • Loss of disinfectant residual and formation of disinfection byproducts.
  • Increased lead and copper levels due to stagnant water increasing corrosion of pipes and fittings.
  • Growth of bacteria in water treatment equipment such as softeners and filters, plumbing fixtures, and hot water heaters that have not been in use regularly.
  • Legionella, a pathogenic bacteria responsible for causing serious and life-threatening diseases, thrives in conditions where water temperatures are moderate. As hot water cools and cold water warms (conditions present in stagnant water of under-used buildings), bacteria, such as Legionella can grow prolifically.

To protect public health, building owners and managers should minimize water stagnation during closures and maintain building water quality prior to reopening. Maintaining water quality may help prevent the need to perform more complex restoration steps. The Department of Public Health recommends the following steps to help mitigate risks and provide a safe water supply.

Steps to Ensure Water Quality


The purpose of flushing the water throughout the facility is to replace any residual and potentially stagnant water in the plumbing with fresh water. Flushing involves opening taps and letting the water run to remove water that has been standing in the interior pipes and/or outlets. Prior to doing any flushing at your building, ensure the water heater has been properly maintained and set to at least 140 degrees Fahrenheit to further prevent the growth of Legionella. Follow the manufacturer’s instructions to determine whether the unit needs to be fully drained after prolonged periods of low use.

  1. Contact your local water utility (Missouri American Water) about the water quality and to coordinate maintenance activities.
  2. Flush the service line that runs from the water main to the building before flushing the rest of the building’s plumbing system.
  3. Start the building’s flushing process closest to where the water enters the building, working your way out to most distant points. Flush hot and cold water through all points of use (faucets, showers, etc.). Cold water should be flushed before hot water. The amount of time needed to flush each point of use may be different depending on the size of the building.
  4. Consider the size and layout of your building when determining how to appropriately flush the plumbing. It may also be necessary to perform this one room or floor at a time depending on the available water pressure.
  5. Flush until the hot water reaches its maximum temperature. Ideally, hot water should reach at least 120 degrees Fahrenheit. Anti-scalding controls and devices may limit the maximum temperature at the point of use.
  6. Flush cold water until temperature stabilizes (at least two minutes).
  7. Attempt to minimize splashing and aerosol generation during flushing. A mask may be worn as an extra preventative measure; a N95 mask is suggested.
  8. Flush all individual fixtures. Toilets should be flushed twice and other faucets/showerheads should be flushed with both hot and cold water for two minutes each. All other appliances (dishwashers, ice makers/refrigerators, drinking water fountains, etc.) should be flushed at full flow for at least two minutes. Refer to the manufacturer’s instructions for any further guidance or when deciding if it is necessary to replace filters.


Clean all water features, safety equipment and sources of non-drinking water (decorative fountains, safety showers, eyewash stations, fire sprinkler systems, etc.). Follow any manufacturer’s instructions for flushing, cleaning and disinfecting these items. Ensure there is no residual slime or biofilm.

Cooling towers - towers and basin should be cleaned and free of slime or biofilm. Ensure that the cooling towers are maintained (including start-up and start down procedures) per manufacturer’s instructions and then proceed with disinfection. For further information, consult CTI guidance.

Spas: Drain, clean and disinfect any hot-tubs or spas. Flush water at source point prior to refilling. Follow the CDC’s recommendations for hot tub and spa disinfection (follow Steps 4–9 and 12–13).


Consider creating a water management plan. The CDC provides a toolkit to assist in creating an ideal water management plan.

Check in with your local water utility (Missouri American Water) to learn if there have been any recent water supply disruptions or to request a check on your disinfectant residual entering the building. After thoroughly flushing the building and achieving optimal water quality, regularly check your water parameters (temperature, pH, disinfectant levels) and follow your water management plan to ensure adequate protection against Legionella.