Current work-at-home orders have resulted in many commercial buildings being under-utilized or even non-operational. These circumstances can impact various building systems, most critically, the potable water system. The non-use of building water creates an extended period where water is not flowing through the system. While there is no information regarding the transmission of novel coronavirus via water, these low/no flow situations present a significant opportunity for the piping system to be compromised with severe corrosion, scale and biofilm, allowing harmful bacteria to proliferate. Often a bio-film can form on wetted surfaces, further impacting disinfection by normal operation. 

For buildings with limited occupancy during stay-at-home orders, a proactive maintenance program may be an effective mitigation practice. Some buildings may have maintenance or security staff on- site through the reduced activity period. A proactive approach in these situations may be for this on-site staff to flush water systems on a regular basis (e.g., five minutes every three to four days) to potentially mitigate the creation of an environment conducive for microbial growth within the water piping system. Nonetheless, caution is advised for the full restart of building water systems.

by Michael L. Walker, PE
Vice President, Principal Engineer

Restarting a Commercial Building Water System
Step one is an assessment. It is imperative you know your water system; its piping configuration and end uses. The objective of the procedure is to flush the entire water system and the effectiveness of this flush/disinfection will be compromised if any portion of the system is not fully flushed. 

Things to note include:

  • Limited use areas and portions of the system farthest from the incoming service connection,
  • The duration of low or under use throughout the system, and
  • Any dead legs (locations where pipe legs end of valves are closed and therefore prevent water flow in that section).

Dead legs in piping configurations cause special concerns and need to be addressed specifically and beyond the scope of this guidance. The best approach to address dead leg issues is to remove them from the piping system.

Since it will be unknown whether pathogens have developed in the water system, caution is advised. For example, minimize splashing by opening valves slowly. Also, use of appropriate Personal Protection Equipment (PPE) such as safety goggles, rubber gloves and NIOSH approved N95 respirators is recommended.

The purpose of building flushing is to introduce chlorinated water throughout the building and provide the necessary contact time to disinfect. It is preferred to flush as many outlets simultaneously as possible, depending on building size and water pressure. Not only is chlorinated water entering the piping, but the higher pipe flow will also assist in removing any bio-film that may have begun to form. For larger buildings, flushing may need to occur in segments (e.g., floors or individual wings) to ensure a good flow of fresh water through individual lines.

To flush a water system or subsystem for building restart, start by opening all water outlet valves, such as faucets and showers (hot and cold), and flushing all toilets and urinals for 5-10 minutes. Outlets farthest from the incoming service connection should be allowed to flush for at least 10 minutes. If there are indications that water stagnation persists after flushing (bad or “off” taste, unpleasant odor or a slight color appearance), repeat flush procedure. 

Don’t forget the end point use devices, such as drinking water fountains, water coolers, bottle fillers ice makers and plumbed coffee makers. All operable end point devices should be flushed for at least 5 minutes. Dispose of any ice in freezers or ice makers.

Any filtration systems associated with these devices (or plumbed into the building system) present additional opportunities for bacterial growth. All filters must be replaced during the flushing of end point devices.

Finally, make sure that your water heater is set to at least 120°F.

How Can We Help?
The EI Group, Inc. is uniquely qualified to support efforts to reopen businesses, from our health and safety personnel on the front lines conducting employee screenings to engineering staff able to assess building systems. Learn more about our capabilities at If you have questions regarding our COVID-19 related services, please contact us at (800) 717-3472 or [email protected].