This column details a recommended flushing procedure for building owners, property managers, water utilities, health officials, code officials, service contractors, engineers, insurance companies and other interested parties to perform within buildings before reopening them for occupancy after a long shutdown. 

With the recent COVID-19 events causing many stay-at-home orders and extended vacancy of offices and workplaces, there is a looming, serious issue associated with stagnant or aging water in unoccupied buildings. Bacteria will grow and flourish in the biofilm of plumbing tanks, fixtures and piping that have been sitting stagnant in ambient temperatures or warm water, where water treatment chemicals have dissipated to levels that will not control bacterial growth. 

Studies have shown that water treatment chemicals dissipate over time. Several factors affect the rate of dissipation, such as pipe material, temperature and organic contaminants in the water. After the chlorine dissipates, bacteria can grow to high numbers. When bacteria and microorganisms are aerosolized in water from showers and other fixtures, they be inhaled into the lungs, causing Legionellosis or Legionnaires’ disease. 

Therefore, it is important to flush these stagnant pipes of bacteria-laden water before re-occupying the buildings that have been vacant while we have worked to contain the virus. 

I have been involved in developing Legionella standards and guidelines with ASHRAE and ASSE and I have spent more than 42 years designing plumbing systems to simultaneously prevent scalding and Legionnaires disease. There are standards for flushing and disinfecting large public water mains but there is no consensus standard for flushing and disinfecting plumbing systems within buildings. 

In early 2020, state government officials, with guidance from health officials, issued stay-at-home orders to keep people from spreading the highly infectious disease. As such, these orders caused many buildings to sit abandoned with little to no water usage for weeks or months. When a building has been empty or unoccupied for an extended period, bacteria such as Legionella and various other bacteria, viruses or disease-causing organisms can be found in the inadequately treated or stagnant water after the water treatment chemicals dissipate. 

It is recommended to flush stagnant water from the piping system before opening the building to occupants. To minimize the chances of transmission of Legionella bacteria and other microorganisms to humans, flushing water from the plumbing fixtures is the easiest, quickest and cheapest way to prepare for occupants to return to the building. 

I am encouraging government officials, health officials, water utilities, code officials and other nonprofits to implement these simple flushing procedures into national, state and local ordinances or guidelines to help protect building occupants from bacteria-laden water upon return to facilities that have been sitting idle for a long time. These entities should use the language in this document and create a local flushing and disinfection ordinance for documentation of flushing procedures. 

The government entities can decide what length of shutdown time justifies flushing based on chlorine or other water treatment dissipation rates in local areas. If a building has been idle for more than four weeks, a Legionella test should be conducted on first-draw water before flushing to determine if a chemical disinfection procedure is needed. Chemical disinfection should be performed on the hot water system before heating the water. 

[Please keep spacing, lines, etc. as they are if possible.]

Domestic Water Systems Flushing Procedure

Building Address: ________________________   Flushing Date: _________

Name of Persons Conducting the Flush Operation:

_____________________________________________________________

_____________________________________________________________

For documenting the flushing operations, follow the tasks outlined below. Building owners or maintenance staff should be advised to perform these flushing operations in all buildings that have been closed for an extended period to reduce the risk of illness and death. The objective is to replace all stagnant water in the potable water system with new water containing a disinfectant residual from the municipal distribution system.

Flushing personnel should wear N-95 respirator masks and personal protective equipment during flushing operations. When performing a flushing operation, complete the procedure in the following sequence:

1. Collect a water sample of first-draw water for testing the water treatment chemical residuals in the building service pipe. Collect it from a monitoring point in the service pipe at or near the meter and backflow preventer or where the service pipe enters the building. Note the water utilities water treatment chemical type. This pre-flush test should serve as a baseline to compare pre-flush water quality with post-flush water quality. 

□ Location _________________________; Free Chlorine Residual: ________ ppm; 

Test By: _________; Time: _________ am/pm

□ Location _________________________; Legionella Test1: ___________ #/ml; 

Test By: ______; Time: ______ am/pm

(Note 1. Conduct a Legionella test if the building has been significantly unoccupied for more than 28 days.) 

If the pre-flush water quality test indicates any water discoloration, odor or other unusual characteristics, note them below:

Notes: ______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

2. Collect a water sample from first-draw water of at least five remote locations within the building to determine the building water chemical residuals. These locations should be documented to serve as a baseline to compare pre-flush water quality with post-flush water quality.

□ Loc. #1 ________________________; Free Chlorine Residual: _________ ppm; 

Test By: ___________; Time: ______ am/pm 

□ Loc. #1 _______________________ _; Legionella Test1: ____________ #/ml; 

Test By: ___________; Time: _________ am/pm

□ Loc. #2 ________________________; Free Chlorine Residual: _________ ppm; 

Test By: ___________; Time: ______ am/pm 

□ Loc. #2 _________________________; Legionella Test1: ____________ #/ml; 

Test By: ___________; Time: _________ am/pm

□ Loc. #3 ________________________; Free Chlorine Residual: _________ ppm; 

Test By: ___________; Time: ______ am/pm 

□ Loc. #3 _________________________; Legionella Test1: ____________ #/ml; 

Test By: ___________; Time: _________ am/pm

□ Loc. #4 ________________________; Free Chlorine Residual: _________ ppm; 

Test By: ___________; Time: ______ am/pm 

□ Loc. #4 _________________________; Legionella Test1: ____________ #/ml; 

Test By: ___________; Time: _________ am/pm

□ Loc. #5 ________________________; Free Chlorine Residual: _________ ppm; 

Test By: ___________; Time: ______ am/pm 

□ Loc. #5 _________________________; Legionella Test1: ____________ #/ml; 

Test By: ___________; Time: _________ am/pm

If the pre-flush water quality test indicates any water discoloration, odor or other unusual characteristics, note them below:

Sampling Notes: __________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

(Note 1. Conduct a Legionella test if the building has been significantly unoccupied for more than 28 days.)

3. Determine the building service pipe size and length. 

Service pipe size: _________ , volume gallons/linear foot 

Service pipe length: _________ 

4. Determine the volume in the building service pipe based upon its size and length in Table 1 and multiply the volume by 2 for the required volume to be flushed from the service piping. 

Service pipe volume from Table 1:  _________ 
(Linear feet of service pipe x volume per foot from No. 3.)

Service pipe volume from Table 1 x 2 = _________ (See Note 2.)

(Note 2. Volume of water to be flushed through the service pipe at 3 feet/second velocity per Table 2.)

5. Determine and document the quantity and location of the fixtures required to be flowed simultaneously to have a velocity of 3 feet/second in the service pipe (see Table 2). From hose valves or fixtures near the service entrance, flow the required number of fixtures or hose outlets to have a flushing velocity high enough to scour bio-film and sediment from the service pipe at a flow velocity in excess of 3 feet/second as determined in Table 2. 

6. Perform and document a pre-flush water quality test at the water service entrance and at five remote fixtures to determine water quality and water treatment residual. There should be a minimum 1 part per million (ppm) free chlorine at the building service entrance and 0.5 ppm of free chlorine at the most remote fixture. 

For buildings with other water treatment chemicals in the utility water, consult with a professional for recommended minimum water treatment chemical levels or as directed by the facilities’ water management program team entering the building. If the test shows the water quality is good, then no service pipe flushing is needed. 

7. If the pre-flush water quality test indicates any water discoloration, odor or lack of sufficient free chlorine residual, perform and document a full velocity flush of 3 feet/second for the building water service pipe as follows: 

a. Determining the proper number of fixtures to flow to flush the building service pipe at a minimum velocity of 3 feet/second, based on the size of the building service pipe size (see Table 2)

b. The flow can be through a combination of fixtures such as hose bibbs, hydrants and fixtures near the water service entrance. Test the potable water service connection until a disinfectant residual is detected or a volume equivalent to double the water held in the service connection is cleared, whichever occurs first.

8. If a disinfection residual is not detected after 30 minutes of flushing the building service pipe, stop flushing and do not continue with the potable water system flushing operation. Contact the water utility for direction and ask to have them or the fire department flush the water mains through nearby fire hydrants to bring chlorinated water close to the building. 

If the building is in a cluster of buildings or area with many unoccupied buildings, there may be a logical place to flush a hydrant near the end of the water main. 

9. When a disinfectant residual is detected on the building service pipe, open some faucets that are the farthest away from the building water service and on the end of each major branch main of the water distribution piping. Let the hot and cold water run continuously until a disinfectant concentration is detected close to or equal to that of the chlorine residuals in the building service connection. 

A branch main is defined as a main distribution pipe (typically greater than 3/4-inch diameter) that supplies other branch pipe and fixture branch pipe. 

10. Flush all remaining fixtures, tanks and appliances connected to the potable water system (including exterior outlets). Flow water from both the hot and cold water systems. The following flushing procedure should be used based on each fixture type:

□ Toilets and urinals shall be flushed five times each for 1.6 gpf fixtures.

□ All other fixtures shall be flushed for a minimum of 3 minutes each, both hot and cold water with flows of 2 gallons/minute.

□ Any water storage or hot water tanks should be flushed at a rate to flow at least two times the volume of the tank.

□ Hydro-pneumatic and thermal expansion tanks should have the water pressure relieved from them so that they totally discharge all water within the tank. 

□ Infrared faucets shall be operated for a consecutive period of time equal to 20 cycles for every 10 feet of 3/4-inch branch piping.

11. The person performing the flushing operation should record the room number, the fixture type and ID, flow rate in gpm, start time and temperature, end time and temperature, chlorine residual near end of flushing operation, and notes or observations for each fixture, such as ambient temperature of the room, when the water temperature starts to change indicating fresh water is arriving at fixture, chlorine residuals in the first draw and at completion. 

This should be repeated until a minimum chlorine residual of 0.5 ppm is achieved at each fixture. Take a water sample in the first draw and upon completion of the flushing, and note any water discoloration, odor, etc. Test the chlorine residual in the final draw at the completion of the flushing operation. 

If the measured chemical residual is insufficient to control bacteria growth, perform and record the flushing operation as shown on the Fixture Flushing Record Sheet. 

12. The water utility has a duty to deliver safe drinking water to the building service meter, according to the Safe Drinking Water Act. Note that utilities are allowed to fall below the level of quality in the safe drinking water act for three consecutive 6-month reporting periods before they must notify the public. 

The responsibility for building water safety is the responsibility of the building owner. The drinking water provider has no responsibility for water quality on the building-side of the water meter. A water utility should strive to deliver quality water, but we know that the water utilities cannot guarantee safe drinking water because there are often water main breaks, construction, fire events and other disruptions of water main flows that cause turbid water and high bacteria events. 

For this reason, the building owner has a duty and responsibility to monitor the water quality coming into the building and have a water management plan in place to address water quality issues. In this day of water conservation, water flows have been reduced to levels that are less than 20 percent of flows prior to 1992. The flow in water mains has been reduced to the point where water treatment chemical residuals dissipate to levels that will not control bacteria growth in the water mains. 

Building owners must monitor the incoming water and adjust the water quality if needed by using supplementary water treatment systems. When a building owner is considering a supplementary treatment system, they should consult with a professional to determine if they licensing, certification and filters are needed. 

13. When a building is unoccupied for more than seven days or a period of time agreed to by the building’s water management program team, flushing should be performed immediately prior to re-occupancy. When a building is unoccupied for more than four weeks (28 days), or a period agreed to by the building’s water management program team, flushing and disinfection should be done immediately prior to the building being reoccupied.

Flush all sinks first, then flush showers, then flush water closets and urinals. Fixtures with flush valves can become clogged with debris and not flush properly if they are flushed first. If flush valves do not perform properly and run on, shut off the water, remove the diaphragm and clean the orifice. When done flushing, remove faucet strainers and showerheads and clean or replace them.

Storage water heaters should be maintained at a minimum temperature of 140 F or higher in the tank to offset heat loss and maintain a minimum water temperature that is a couple of degrees above the Legionella growth temperature of 122 F (124 F on the hot water return pipe connection to the water heater). 

Hot water temperatures can be higher in the storage and distribution piping and should be reduced or limited at or near the fixtures by code-compliant temperature limit-stop. These should be properly adjusted on tub/shower valves or by temperature-limiting valves that are properly set to limit temperatures at the point of use. 

Every fixture in the building should be flushed in accordance with these guidelines or until the water treatment chemical residuals reach an acceptable level. Following these procedures should prevent thousands of workers from getting sick and dying from Legionnaires disease and other types of waterborne illnesses associated with stagnant water.