Water quality frequently asked questions

If Legionella is found in the water, can we still use fixtures? If so, why is that considered acceptable, as it seems counterintuitive?

Despite the presence of Legionella, people can still use fixtures without ill effects, This is a common practice in high-risk facilities, such as hospitals and nursing homes, according to public health guidance. Regular using (flushing) fixtures, with established preventive measures like following flushing protocols and maintaining proper water temperatures, is essential for reducing Legionella growth and maintaining water quality.

Taking fixtures out of service can actually makes the problem worse by allowing water to sit stagnant, which promotes bacterial growth. Thus, taking fixtures out of service is counterproductive and can lead to higher risk in the long run. Public health agencies, including the CDC and ASHRAE, recommend maintaining fixture use along with appropriate water management practices to control Legionella, ensuring water systems remain functional and safe. These guidelines, which align with ASHRAE 18 and the CDC’s Legionella prevention toolkit, emphasize proactive management to reduce Legionella proliferation while keeping fixtures in use.

Are buildings with elevated levels of Legionella safe?

Buildings with elevated Legionella levels are still safe to occupy while appropriate control measures are being used. The CDC considers a high level of Legionella to be 1 CFU/mL or higher, as this may indicate conditions that could support bacterial growth. However, address extensive colonization to reduce risk, especially in areas that treat or house high-risk populations (such as hospitals or nursing homes) and in locations where large amounts of water are in the air as a spray, such as cooling towers, spas, or decorative fountains.

Is it safe to use the water for washing hands or dishes after receiving positive results for Legionella, lead and copper, or Total Coliform/E. coli?

Legionella: Water can be safely used for handwashing and dishwashing, as these activities typically do not generate aerosols. Cold water can also be used since Legionella thrives in hot water plumbing.

Lead and Copper: Use only cold water for drinking and cooking, as hot water increases metal leaching. Flush cold water before use and avoid ingestion. Non-ingestive uses, such as handwashing and dishwashing, pose no risk.

E. coli or Total Coliform: Do not use the water for any purpose until it has been treated and confirmed safe.

What is Legionella? Why is it found in water systems?

Legionella is a naturally occurring bacterium commonly found in man-made water systems. It can enter through natural water sources like lakes and streams. It thrives in warm, stagnant areas of water systems, multiplying between 68°F and 122°F (20°C and 50°C).

What is Legionnaires’ disease? What symptoms should people be aware of?

Legionnaires’ disease is a severe form of pneumonia caused by inhaling water droplets containing Legionella bacteria. Symptoms include cough, shortness of breath, fever, muscle aches, and headaches.

How do people contract Legionnaires’ disease from Legionella in water?

People contract Legionnaires’ disease by inhaling small water droplets (aerosols) contaminated with Legionella, typically from showers, cooling towers, or other devices that spray water drops.

What is the risk of contracting Legionnaires’ disease from various water fixtures, such as showers, drinking fountains, and kitchen and bathroom sinks that supply drinking water?

The risk of illness from Legionella remains very low. Few cases of Legionnaires’ disease occur, despite its common presence in water systems. However, we still take proactive measures to address underlying factors and reduce potential risks.

If representative sampling was used and the outlets in my area weren’t tested, how can you ensure the water is safe, especially if other outlets in the building tested positive?

Representative sampling enables GSA to identify trends and potential risks for Legionella growth in the water system. An exceedance does not indicate unsafe water. Instead, it highlights conditions that may promote Legionella growth at specific outlets. To stop that growth, we may use measures such as flushing, operational adjustments, treatment, or system-wide disinfection.

Why is GSA conducting representative sampling instead of testing every outlet in the building? How does this approach compare to practices in other industries, like hospitals?

GSA uses representative sampling to monitor water quality efficiently and effectively. Testing every outlet disrupts daily operations, and costs in money and time. Representative sampling focuses on high-risk areas based on factors such as water temperature, usage patterns, and plumbing layouts. This approach is similar to that used in hospitals, where they test critical areas like patient wings and operating rooms first.

Why is baseline testing for water quality important?

Baseline testing establishes the current condition of a water system, serving as a reference for identifying future changes or issues. By identifying contaminants or bacteria, such as Legionella, building managers can take control measures to maintain safe water quality.

Why is GSA not testing the toilets? Can Legionnaires’ disease be contracted from the water during flushing?

Legionella bacteria primarily pose a risk when inhaled via water droplets in the air. That’s why we priotitize showers and cooling towers are prioritized for testing. Toilets are not typically a risk, as the bacteria are not sufficiently aerosolized during flushing. Also, toilets use cold water, which limits the growth of pathogenic Legionella. For these reasons, toilets are not included in standard Legionella testing protocols.

No industry standard guidance recommends routine sampling of toilets or urinals for Legionella. According to the American Industrial Hygiene Association, even during a cluster or outbreak investigation, toilets and urinals may remain in service, as they have not been known to transmit Legionnaires’ disease. Similarly, the CDC’s environmental Legionella testing protocol does not include toilets or urinals. While a public health authority may choose to sample toilets or urinals during an outbreak investigation—only after ruling out all other potential sources of Legionella exposure—this approach does not apply to the routine sampling procedures GSA conducts.

Is Legionella bacteria commonly found in building water systems? Have studies been conducted on this topic? Could it also be present in my home, church, or school?

Legionella is commonly found in building water systems, even well-maintained ones. Studies indicate it is present in approximately 50% of large building water systems. It is considered a normal part of plumbing system “microbiomes” or bacterial communities. However, despite how widespread Legionella is, Legionella-related infections are rare, accounting for only a small portion of community-acquired pneumonias. Infection requires a pathogenic Legionella strain, sufficient exposure, and a susceptible individual.

If Legionella is commonly found in building water systems, why isn’t Legionnaires disease more widespread?

While Legionnaires’ disease cases occur across all U.S. states and many other countries, infections are relatively rare. For infection to happen, a susceptible individual must inhale enough quantities of pathogenic Legionella. Most water uses—such as drinking, handwashing, and toilet flushing—pose minimal risk since they do not create conditions for inhaling aerosolized droplets. Elderly individuals or those with weakened immune systems are more susceptible to infection.

When should I get tested for Legionnaires’ disease? What are the different testing methods available to confirm a diagnosis?

If you are diagnosed with pneumonia, public health guidelines recommend requesting a Legionella diagnostic test. Diagnostic methods include urine antigen tests, respiratory cultures, and blood tests. However, if you are not experiencing symptoms of pneumonia, public health experts do not recommend testing for Legionnaires’ disease, as it is unnecessary unless you are ill.

Should all the different groups of people identified in the CDC’s high-risk categories be equally concerned, especially considering that many individuals in our buildings are over 50 but relatively healthy?

Relatively healthy individuals over the age of 50 face a lower risk of illness than those with highly compromised immune systems. Still, if you are experiencing symptoms of pneumonia, check with your medical provider.

If I fall into one of the high-risk categories and Legionella has been detected in my building, what steps can I take to reduce my risk of developing Legionnaires’ disease?

If you are at high risk, consult your medical provider. If you experience symptoms of pneumonia, the CDC suggests requesting a Legionella diagnostic test. Legionnaires’ disease is treatable with antibiotics. As a precaution, the CDC recommends avoiding activities that create water mist, such as showering, or using cold water to reduce aerosolization risk. Also, take care not to make a mist when using water—for example, by filling sinks slowly.

Is it required or even common practice for most building owners to conduct regular water testing on their plumbing systems, or is GSA’s initiative to conduct a large-scale assessment unique?

Water testing within buildings is not typically required. Water testing within buildings is usually conducted only when illness is linked to a building or in higher-risk facilities, such as healthcare settings. Until recently, the CDC did not recommend Legionella testing even for healthcare facilities. The General Services Administration’s (GSA) proactive large-scale assessment goes beyond standard requirements. As we know more about waterborne pathogens like Legionella grows, we’re doing more regular testing. We hope this initiative inspires other large property management firms to do the regular testing we’re doing.

When is a water management plan recommended?

A water management plan is recommended for buildings with complex plumbing systems, especially those serving high-risk populations like hospitals and nursing homes. These plans help maintain consistent water quality by identifying and managing risks, including bacteria such as Legionella.

What are the major growth factors that allow Legionella to thrive within a water system? What are the best practices for keeping the situation under control?

Legionella thrives in warm, stagnant water, particularly in systems with biofilm (slimy layers in pipes) or scale. Water management and engineering controls can minimize its growth by maintaining proper water temperatures, ensuring water flow, and cleaning fixtures regularly.

What common remediation measures reduce concentrations of Legionella in water systems?

Common remediation measures include flushing the water system, raising water temperatures, and implementing other engineering controls. If Legionnaires’ disease cases are linked to a building, health departments may recommend more measures such as chemical treatments.

When are filters recommended? Can you recommend types of filters that reduce exposure to lead, copper, Legionella, and total coliform in drinking water?

Filters for Legionella are typically only recommended during active outbreaks or in areas with highly vulnerable individuals, such as transplant wards.

• Legionella and Total Coliform: Use filters rated for microbial reduction with a pore size of <0.2 microns.
• Lead and Copper: Use point-of-use filters with NSF/ANSI Standard 53 certification.

Why isn’t the air being tested for Legionella? Is there a risk of Legionella spreading from cooling towers?

Testing air for Legionella is not recommended because results are unreliable. Testing water is far more accurate. Legionella spreads through water aerosols, not air. Cooling towers, which release aerosolized water droplets, can spread the bacteria. To manage this risk, buildings with cooling towers use measures like drift eliminators, maintaining proper distances between towers and air intakes, and installing MERV filters. Also, water that could aerosolize is tested for Legionella as a more reliable detection method.

If fixtures remain in service, is there a maximum concentration of Legionella at which it becomes unacceptable to continue using them?

There is no universally defined concentration of Legionella at which fixtures must be taken out of service. Routine testing identifies whether Legionella is present and provides insights into the system’s performance. Exceedances indicate conditions that may support bacterial growth but do not necessarily mean the water is unsafe.

Fixtures can typically remain in use even when Legionella is detected, as the risk of illness is generally very low. Taking control measures such as flushing, adjusting system parameters, or disinfection can manage growth. Removing fixtures from service is not commonly recommended, as this can create stagnant conditions that promote further bacterial growth. Decisions about continued use must consider the level of risk, the population served, and the ability to take appropriate controls.

How are confirmed cases of Legionnaires’ disease reported? How does the public health department identify the infection’s source?

Legionnaires’ disease is a reportable disease. Healthcare facilities and physicians are required by law in most states to report cases to the local and state health departments. That data is then sent to the CDC. The process of reporting varies from state to state and local health departments define the timeframe within which the case must be reported. If a person with Legionnaires’ disease is associated with a facility, the health department will contact the facility for more information to determine if a case investigation is required. These involve testing the suspected water sources, reviewing building water management plans, and checking for other cases.

Is it possible to fully and permanently remediate Legionella in a water system, achieving a consistent concentration of 0.0 CFU/mL in a system that was previously positive for Legionella?

Completely eliminating Legionella from a building’s water system is nearly impossible due to its natural occurrence. However, totally eliminating Legionella is not necessary to protect public health. Remediation efforts can significantly reduce Legionella levels, but ongoing water management is crucial to prevent regrowth.

If Legionella was detected in my building’s water, is this a result of low occupancy or has it likely been present for a long time without causing any ill effects?

In many buildings, Legionella has likely been present since their construction without causing illness. However, the low occupancy levels created prolonged water stagnation (low water usage) and improved conditions better for bacterial growth.

Is the rise in GSA buildings with positive Legionella results due to an actual increase in the bacteria’s presence, or is it simply because GSA has done more testing and identified it?

The recent GSA water quality testing serves as a baseline for its building inventory, representing a snapshot in time rather than an increase in Legionella growth. Legionella has likely been present for years, as it is in millions of buildings across the country. While low occupancy-related stagnation may have contributed to growth, this initiative provides a starting point for proactive water quality management.

CDC guidelines state that concentrations of Legionella in a drinking water system are performance indicators rather than direct measures of risk to human illness. What does this mean? How does explain allowing fixtures to remain in service?

Routine testing for Legionella provides information about whether Legionella is present and/or growing in the system. If testing targets are exceeded, it does not mean the water is unsafe. In the case of Legionella, an exceedance provides some information about the water system’s function. However, no correlation to concentration and disease risk has been made, as most people are likely exposed to Legionella almost every day. Test results reflect how well the system is operating. They are performance-based indicators, not health-based risk thresholds. Legionella in water systems is common, yet disease due to Legionella is rare. This is why fixtures can remain in use.

What does a Legionella antibody test confirm? Does a positive result show that I have Legionnaires’ disease?

Legionella testing can involve different methods, each serving a unique purpose:

• Antigen Test: This test, performed on a urine sample, detects the presence of Legionella antigens. It can confirm an active infection caused by certain types of Legionella bacteria. It provides quick results but only identifies specific Legionella species, such as Legionella pneumophila serogroup 1.
• Antibody Test: This blood test measures antibodies to Legionella, which indicate past exposure but do not confirm an active infection. Many individuals may test positive without experiencing Legionella-related illness. For a definitive diagnosis using antibody testing, two blood samples are typically needed—one taken during illness and another 8–12 weeks later to assess changes in antibody levels over time.

Both tests serve as part of a broader diagnostic approach, with urine antigen tests being more commonly used to rapidly identify active infections.

I hear a lot about supplemental disinfection systems; why don’t we just install those?

Supplemental disinfection systems can help manage Legionella but are not a one-size-fits-all solution. These systems require proper maintenance and monitoring, and may damage a water system if not managed correctly. They are most effective when basic engineering controls, such as maintaining water movement and proper temperatures, are already in place. Thus, they are generally not recommended as the first step for corrective actions. They can be a second step.

Bibliography

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