The focus of this guidance is to reduce Legionella growth and other pathogen and corrosion concerns that occur when there is a large drop in building water use. The guidance focuses on potable water systems inside larger buildings with complex plumbing and the information is general in nature. Each building is different and will require different actions based on its plumbing systems, use patterns, and source of water supply.
Please see the department’s Guidance for Shutting Down and Reopening Water Recreation Facilities for information about how to maintain and treat pools and spas. More information about cooling towers and HVAC systems can be found on the New York State’s Department of Health webpage. You may also want to make sure that the buildings p-traps do not dry out. You can do this by flushing water down all drains to prevent sewer gas intrusion into the building.
What is the problem and who does it apply to?
Many buildings are closed to the public or have limited access in order to help slow the spread of COVID-19. The resulting drop in building water use increases the risk for Legionella growth in building plumbing and associated equipment like cooling towers, pools, decorative fountains, hot tubs and other equipment. To prevent Legionella growth, these systems must be actively managed and maintained.
If Legionella grows during low use periods, building users have a higher risk of contracting Legionnaires’ disease and Pontiac Fever during the shutdown and when full use resumes. While Legionella is a primary risk, other opportunistic pathogens (Mycobacterium avium) and corrosion concerns (lead scale release) are increased by closure or reduced use situations.
Building closures and reduced occupancy affect all environmental systems operating inside buildings including 1) potable and non-potable water systems, 2) cooling towers and 3) heating, ventilation and air conditioning (HVAC) that regulate interior relative humidity and control mold. These systems must be actively managed and maintained to protect the health of building users. In addition to managing systems during shutdown periods, building owners and operators need to implement well thought out start up protocols to ensure public health protection. By implementing procedures now, you can protect the public and minimize the steps needed to safely re-open closed or partially closed facilities.
Key points about Legionella risk and building water systems in Washington State
Prior to the start of the COVID-19 pandemic, Legionnaires’ disease sickened and killed more people in the United States than any other reportable waterborne disease.4
Legionellatransmission occurs primarilythrough breathingin contaminatedaerosols into the respiratorysystem.
The optimum growth range for Legionella is between 77°F (25°C) and 108°F (42°C),
however, Legionella can survive and grow outside of this temperature range. To reduce bacteria growth, keep hot water systems above 122°F (50°C) at all fixtures and cold water systems below 74°F (23°C). Always follow plumbing and safety standards to prevent scalding at the point of use.
Loss of free and total chlorine residual in building plumbing as a result of stagnant or very low water use is a significant factor that allows Legionella bacteria to flourish.
Nearly all large and medium sized municipal water systems in Washington State use free chlorine for both primary disinfection and for distribution disinfectant residual (secondary disinfection). The only exception uses chlorination for secondary disinfection, which is also very effective against Legionella. If you are not sure if your water system is disinfected, please contact your water utility.
Microbial disinfection of water using free chlorine depends primarily upon the concentration of free chlorine and time. Temperature and pH also impact chlorine disinfection efficiency against microbes. ‘CT’ is the term used in the drinking water industry to quantify disinfection. C stands for ‘concentration of free chlorine in mg/L units’.T stands for timein minutes. Example: Free chlorine residual of 50 mg/L held in piping for 120 minutes (2 hours) equals a CT of 6,000 mg-min/L.
Recommended Monitoring and Management of Building Water Systems
Monitoring building water quality
Because temperature and chlorine residual are primary factors affecting Legionella presence in building plumbing, DOH strongly recommends that temperature and chlorine residuals be accurately measured and used to manage building water age. All building water systems should have an accurate digital chlorine residual test kit that uses an EPA-approved test method for use in drinking water compliance.6,8 Test strips and color wheels are not accurate and not recommended testing methods for water systems. Thermometers should be accurate to within
+/- 1°C. Operators should measure daily chlorine residual and temperature of water entering the facility from the water utility supplier. Chlorine concentrations in building plumbing will be
Less than or equal to utility concentrations. Building cold water temperatures will be equal to or higher than utility temperatures.
Maintaining systems under low use conditions (but not closed)
Starting up building water systems after closures and sustained low use
To ensure you and your employee’s safety from both chemical and biological exposure while disinfecting and flushing the building plumping, appropriate training and PPE should be considered. You can find guidance on worker safety for Legionella control and prevention on the OSHA website.
Academies of Science4 for testing of Legionella in water. Collect samples at least 48 hours after final flushing and return of normal operation of the water system. Samples collected
too early may give false negative results1. Collect samples from critical locations9. (CDC
toolkit) The CDC maintains a list of labs certified for legionella testing called ELITE labs. Other labs may be available in your area that are not on the CDC ELITE list of labs. Discuss with the labs if their method is suitable for conducting environmental testing of water for Legionella.
Legionella in Water Systems. Washington, D.C. The National Academies Press.
Washington State Department of Health
Department of Health https://www.doh.wa.gov/portals/1/Documents/pubs/331-
Department of Health and Human Services CDC
Water, Purdue University Center for Plumbing Safety
12 Building Water Quality and Coronavirus: Flushing Guidance for Periods of Low or No Use, Environmental Science Policy and Research Institute
Section 3.185 Table 6: European Union Action Levels for Legionella in Potable Hot and Cold Water Systems
Not Detected < 100 to 1,000
Acceptable – continue monitoring
Refer to responsible person and assure water quality values are within target
> 1,000 to < 10,000
i) Resample ifsmall percentage(10-20%) are positive; review control measures
ii) If >20% positive may indicate low level colonization, disinfection of system,and risk assessment to determine additional actions
Resample, immediate review of control measures, disinfection of whole system
Source: EU (2017).
The EU guidelines emphasize the goal to achieve no cultural Legionella, but acknowledge that
occasional detection (<20%) of low levels of Legionella (< 1,000 CFU/L) may be acceptable
provided that other water quality values (e.g., temperature, disinfectant) and operational parameters are within the water management plan guidelines. Intermediate levels (> 1,000 to
< 10,000 CFU/L) and high levels (≥ 10,000 CFU/L) trigger a series of actions including resampling, remedial measures such as disinfection, and overall review of the water management plan program.
More COVID-19 Information and Resources
Stay up-to-date on the current COVID-19 situation in Washington, Governor Inslee’s proclamations, symptoms, how it spreads, and how and when people should get tested. See our Frequently Asked Questions for more information.
The risk of COVID-19 is not connected to race, ethnicity or nationality. Stigma will not help to fight the illness. Share accurate information with others to keep rumors and misinformation from spreading.
Have more questions about COVID-19? Call our hotline: 1-800-525-0127. For interpretative services, press # when they answer and say your language. (Open from 6 a.m. to 10 p.m.) For questions about your own health, COVID-19 testing, or testing results, please contact your health care provider.