Conversations about Legionella often revolve solely around mitigation design methodologies in the plumbing engineering realm. However, focusing solely on these methods neglects a critical aspect of risk management within buildings.

First published in 2015, ASHRAE Standard 188, Legionellosis: Risk Management For Building Water Systems, was a pivotal development in the United States. This standard set the benchmark for legionellosis risk management, targeting those tasked with maintaining building water systems. It delineates the essential components of a water management program (WMP), a cornerstone for compliance for any facility required to establish policies and procedures to reduce the risk of growth and spread of Legionella.

Understanding WMP elements, established in ASHRAE 188, is pivotal in designing plumbing systems that curb Legionella growth and streamline compliance tasks for facility managers.

• Preventability and liability. The advent of ASHRAE Standard 188 marked a turning point, particularly in terms of liability. Its establishment of an industry-wide standard of care for managing legionellosis risks within building water systems significantly impacted legal proceedings. With this standard in place, prosecuting negligence became more straightforward, elevating concerns about liability among building owners and operators.

• Insurance scrutiny. With the increased liability concerns, U.S. insurers are beginning to intensify precautions related to Legionella risk before adding new clients or renewing coverage. According to Reuters, insurers might limit Legionnaires’ Disease coverage amounts or impose higher deductibles if building systems are outdated (https://bit.ly/3vsrmYs). 

• Expanding compliance requirements. Initially limited to certain health-care facilities, compliance requirements have expanded to include various sectors, such as K-12 school districts, government buildings, and WELL v2 certified buildings. Even businesses such as Marriott International voluntarily adopt WMPs to mitigate financial risks and ensure safer water systems.

Water Management Elements

1. Establish a water management program team. 

Team members may include:

Facility executives/administrators;

Facility managers or plant operators;

Safety officers;

Equipment or chemical suppliers;

Contractors/consultants (e.g., water treatment professionals, engineers, etc.);

Certified industrial hygienists;

Microbiologists;

Infection control specialists;

Environmental health specialists;

State and local health officials.

2. Describe the building water systems using text and flow diagrams (See Figure 1).

3. Identify areas where Legionella could grow and spread. Perform a hazard assessment and determine the severity of risks. (See Figure 2).

4. Decide where control measures should be applied and how to monitor them (See Figure 3).

5. Establish ways to intervene when control limits are not met. What corrective actions did you perform?

6. Make sure the program is running as designed and is effective.

7. Document and communicate all activities.

Once you understand the elements of a WMP, you can identify where to implement design methods to facilitate compliance. 

The remainder of this article focuses on fundamental controls, monitoring hot water temperatures and ensuring disinfectant. Refer to Table 1.1 for industry requirements and recommendations concerning water quality monitoring and compliance (See Figure 4).

Maintaining Temperatures

Maintaining cold and hot water temperatures outside the Legionella growth range are important means of managing risks. However, according to Dr. Janet Stout of the Special Pathogens Laboratory, the system of most concern for Legionella amplification is the domestic hot water system; therefore, let’s explore maintaining domestic hot water temperatures.

Outside of physically holding a thermometer under a stream of water, there are three options for monitoring water temperatures, which is required in most WMPs.

1. Independent temperature sensors or gauges. These can be analog or digital, intended for temperature monitoring only. Digital sensors can be integrated into the building automation system (BAS) or cloud-based, providing remote access. These sensors provide 24/7 monitoring, alerts, data logging and digital documentation. In contrast, analog gauges require manual verification, are not BAS-integrated, and rely on facility staff to read and record temperature data at scheduled intervals.

2. Temperature-actuated mixing valves. A key system component found in most large hot water systems. Temperature-actuated mixing valves allow users to generate and store at temperatures higher than safely allowed through the fixture tap. Thermostatic or digital mixing valves are the most common in commercial construction. 

While the valve’s primary function is to prevent scalding and ensure temperature safety, they are often used in many facilities as the primary source for temperature monitoring. While thermostatic valves provide an analog temperature gauge on the water outlet, digital valves provide digital sensors for inlet and outlet temperatures, as well as BAS connectivity, digital documentation and programmable control.

3. Balancing valves. This is easily the biggest challenge to maintain water temperatures in a building. Without proper hydraulic balancing, you cannot control or maintain consistent temperatures. The most recent version of ASHRAE Guideline 12, Managing the Risk of Legionellosis Associated with Building Water Systems, and the newly published ASHRAE Standard 514, Risk Management for Building Water Systems: Physical, Chemical, and Microbial Hazards, recommend temperature monitoring at each hot water return loop in the system. 

This allows the facility to verify temperature control limits are being met throughout the system. While multiple balancing valve solutions are on the market, selecting a valve that provides an analog temperature gauge or BAS sensor is necessary to meet temperature monitoring compliance. As with other digital products, digital balancing valves provide the most monitoring, documentation and control features. 

Ensuring Disinfectant 

Routine purging or flushing of piping mains, branches and fixtures is a common operational practice relatively unknown to many plumbing designers. However, numerous standards and guidelines recommend routine flushing procedures as a fundamental control measure. The World Health Organization states that Legionnaires’ Disease prevention depends on applying control measures, including “reducing stagnation by flushing unused taps in buildings on a weekly basis.” 

Here are a few other examples:

1. American Society of Plumbing Engineers, “Engineering Methodologies to Reduce the Risk of Legionella in Premise Plumbing Systems,” 3.1.3 Water Age/Disinfectant Residual/Flushing

A flushing protocol of distal sites can keep more disinfectants in the water by drawing in fresh water with a higher residual disinfectant level.

2. Veterans’ Health Administration, VHA Directive 1061, 3.d. Flushing

The purpose of routine flushing is to prevent stagnating conditions in piping that could result in tempering of water temperature, dissipation of biocide and establishment of favorable conditions for Legionella growth.

3. ANSI/ASHRAE Guideline 12, Section 5.3.4 Routine Flushing 

Routine flushing is the control measure most often used to help reduce water age.

4. The National Academies of Sciences Engineering Medicine, “Management of Legionella in Water Systems” (2019)

Periodic water flushing is particularly useful to prevent colonization and limit the growth of Legionella at the distal sites of cold- and hot-water systems.

Remember that a control measure, such as routine flushing, must have established control limits, a means of monitoring and procedures to verify the program is running as designed. Are you incorporating these types of controls, monitoring and documentation into your plumbing designs?

As the industry’s understanding has grown, so has the availability of products designed to simplify and facilitate the practice of routine flushing along with the associated data/documentation compliance.

Engineered Products to Support Flushing Compliance

1. Auto-flush fixtures. A growing list of sensor faucet manufacturers offer products that will allow the purging of stagnant water automatically. Each provides different options for programming, information management, purge frequency, purge duration, purge velocity and temperature control. 

When selecting an auto-flush fixture, an engineer should keep in mind that there is a difference between an existing product portfolio modified to perform a function and a product developed for it. A product such as the Rada digital faucet is an example of a product made for a specific application and provides a greater range of auto-flush options to meet specific project needs. 

Due to costs, auto-flush fixtures may not be a reasonable solution to implement at every fixture, and this is where an auto-flush device may be a better alternative to meet the flushing objectives.

2. Auto-flush devices. Auto-flush devices are often used when a facility seeks to maintain disinfectant residual within established control limits throughout the piping distribution system. They may be located at the ends of pipe mains, branches, seldom-used bypasses or hot water storage tanks. 

Two types of auto-flush devices on the market are stand-alone devices, best when only one or two locations are required, and centrally controlled systems, where several devices are placed throughout the entire facility. 

Stand-alone devices can be as simple as a solenoid valve set to an analog timer. Due to their simplicity, they often have limited control options, a single trigger to initiate a purge and little to no monitoring or documentation features.

Centrally controlled auto-flush systems, such as the Hycleen Automation System by Georg Fischer, provide multiple triggers to initiate a purge, have customizable frequency and durations, real-time monitoring, data-logging, alerts and multiple control options. 

As you can see from Table 2.1 and Table 2.2, the purge frequency, duration, velocity and volume of auto-flush fixtures are significantly lower than auto-flush devices. Identifying a facility’s goals for routine flushing allows you to select the best-engineered solution for their specific system. 

Distinguishing between Legionella mitigation design methodologies and water management compliance is crucial. Compliance revolves around managing risks, irrespective of design methods. Understanding the elements of a WMP is key to designing systems that meet compliance requirements while reducing Legionella risks.

To meet compliance and operational needs, plumbing engineers must integrate specific controls, monitoring mechanisms and documentation procedures into their designs. This includes:

• Working with the program team to understand the control measures, control limits and desired verification method.

• Provide means of verification by selecting manual, analog, BAS-integrated or cloud-based instrumentation for control limit verification. Keep in mind that manual verification places a burden on staff. It requires time, diligence and knowledge.

• Provide means of data logging and documentation, a critical part of any WMP to verify, benchmark, assess and manage risks.

• Consider engineered products that automate operations, provide real-time data and simplify documentation requirements.

Understanding the fundamentals of water management programs is paramount for plumbing engineers. It not only facilitates the reduction of Legionella risks but also ensures that systems align with operational compliance requirements. By incorporating these principles into Legionella mitigation methods, engineers can pave the way for compliant-friendly plumbing systems in the future.

Greg Swafford is a principal at Smith Seckman Reid and a seasoned professional with more than 25 years of engineering and manufacturing experience. As a trusted advisor, consultant, writer and speaker, he actively contributes to industry standards and best practices in Legionella water safety and management.