How to safely flush plumbing systems and re-open facilities after shut-down

by Jeremy Overmann, Chemist & Water Treatment Specialist
ISTC Institutional Water Treatment services group

The domestic plumbing systems in any building or part of a building that has been shut down or has experienced reduced use due to COVID-19 policies are at risk for causing disease and death due to the effects of increased water age, including corrosion and growth of bacteria. Before re-opening any such building, take steps to minimize these risks and include consultation with a licensed plumber.

The Illinois Department of Public Health (IDPH) has a general guidance document for returning these systems to regular use. In Attachment B (Section II, Step 2. b), IDPH recommends setting the water heater to at least 120 degrees F prior to flushing the domestic hot water plumbing.

We recommend a higher temperature of at least 142 degrees F as this will kill Legionella bacteria in the heater within 30 minutes. However, do not use water at this temperature for flushing if the building’s drain waste vent (DWV) materials and/or plumbing system components cannot handle this higher temperature.

WARNING: 142 degree F water can cause third degree burns in seconds. Note that Legionella bacteria can continue to grow at temperatures up to 122 degrees F.

The Environmental Science Policy and Research Institute has written a useful guidance document, Reducing Risk to Staff Flushing Buildings, which offers best practices for flushing building water systems in a way that keeps facility staff safe.

Use the IDPH guidance in conjunction with your facility’s Legionella Water Management Program (WMP). If none exists, we recommend writing a remediation and/or recommissioning plan, then later developing a full WMP. The Centers for Disease Control (CDC) offers a free training program on how to write a WMP and a toolkit to assist in developing a WMP.

Additional recommendations

Drinking Fountains: If these were shut off and/or not used for a period of time, they should be cleaned according to the manufacturer’s instructions before being used again for drinking.

Chlorine levels: The Illinois EPA requires a minimum of 0.5 parts per million Free Chlorine or 1.0 parts per million Total chlorine (also called Combined chlorine) in drinking water, unless a facility has been given an exemption (this is rare, but applies in some cases to facilities supplied with clean well water).

After re-opening, we recommend maintaining 142 degrees F or higher in all domestic water heaters and storage tanks, and 124 degrees F or higher in all recirculating domestic hot water systems for the purpose of reducing the risk of Legionnaire’s Disease. Note that delivered water at fixtures must meet local and state plumbing codes for maximum safe temperature to prevent scalding. The best way to achieve Legionella risk reduction and anti-scalding is to maintain high temperature in tanks and recirculating systems and employ thermostatic mixing valves just prior to point of use fixtures.

Finally, we recommend documenting all actions you take to prepare facilities for re-opening.

For more information

About the Institutional Water Treatment services group

The Institutional Water Treatment (IWT) services group, a unit of the Illinois Sustainable Technology Center at the University of Illinois, provides unbiased, professional water treatment advice to facilities equipped with industrial water systems including cooling towers, chillers, boilers, etc. If you need assistance with addressing system start-up due to COVID-19 or other related services, including legionella monitoring, please contact Jeremy Overmann  or Mike Springman.

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