Two Things to Know About Legionella Sampling Best Practices

Written by: Hilary Nardone, Lead Environmental Group Manager

This time of year, the days are longer, the temperature is warmer, and that means an increased risk of Legionella bacteria in your building water systems. Warm, humid summer days create the ideal condition for Legionella bacteria to amplify in natural, fresh waters and make it more difficult to control the bacteria in domestic water piping. Therefore, it’s a particularly important time of year to prioritize Legionella bacteria sampling in your building water systems.

What are two things everyone should know about Legionella bacteria sampling best practices?

1. Where do I sample and how many samples should I take?

One of the most significant considerations in choosing meaningful sampling sites is to ensure that the entire facility is represented. Equally essential is to identify sources where people could be exposed to Legionella bacteria such as faucets, showers, ice machines, spas, and whirlpool baths. In healthcare facilities, it is particularly crucial to take samples from areas that house susceptible populations including but not limited to NICU, respiratory therapy, cancer treatment, and organ transplant units.

To get full representation of the facility, the New York State Department of Health recommends1 sampling three hot water samples per floor, with no less than 10 samples per hot water recirculation loop.For each floor, the three samples are normally done as follows: tap closest to the first delivery of hot water from the riser; one sample from the middle of the system; one sample from the last outlet before the water returns to the heater. Additionally, samples should also be taken at the building’s potable water point of entry, each hot water storage tank, as well a one water sample from the return piping of the circulated hot water and one water sample from the outlet of the hot water heater. Outside of New York State, these recommendations have become the “gold standard” for the number of samples in a building.

It is also important to test a representative sample of ice machines and whirlpool baths (including birthing tubs) and all spas and decorative water features. Some facilities are opting to test swimming pools, as well.

Remember: Your cooling tower system should be tested, too. Each cooling tower system should be tested quarterly for Legionella bacteria.

2. How often should I be sampling?

It is generally recommended to sample your domestic water every 90 days. In New York State, health care facilities must test quarterly for the first year of testing. Sampling at hematopoietic stem cell transplant and solid organ transplant units especially must be performed quarterly.

Spas, pools and decorative fountains should also be tested quarterly.

Each cooling tower system should be tested every 90 days during its operational season. This is law in New York State for all cooling towers.

Barclay can help!

Barclay offers a full array of Legionella bacteria sampling services, including tracking and trending results, and automatic sampling reminders.

Be sure to contact Barclay Water Management, Inc. for all your Legionella bacteria management needs!

[1] New York State Department of Health. (April 2019). Environmental Health Information Related to Legionellosis in Healthcare Facilities. Available at: Accessed May 2019.

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