The number of Legionnaires’ disease cases reported to the U.S. Centers for Disease and Control Prevention (CDC) has been on the rise for two decades (https://bit.ly/3rhUPzz). As the number of cases continue to rise, so does the need to manage the risks associated with premise plumbing systems.

In recent years, there has been an increase in Legionella awareness as multiple stakeholders have entered the conversation – government organizations, water utilities, health professionals, local jurisdictions, model code bodies, industry organizations, manufacturers, engineers, academic scholars, Legionella consultants, water treatment professionals, etc. These stakeholders hold conferences, attend seminars, create standards, develop guidelines, establish best practices, write research papers, manufacture products, and introduce model code changes. 

Through the individual efforts of stakeholders enough is known about the bacteria and its transmission to successfully control growth in premise plumbing systems; however, with the continued rise in reported cases a comprehensive implementation of control strategies involving multiple stakeholders is necessary.

Most of the resources and standards available focus solely on water management plans and actions by facility operations staff. While this is certainly a critical component to managing risks, it overlooks the tremendous impact that comprehensive plumbing design can make in supporting key water management principles. Design professionals are essential to managing risks. Before diving into how to manage risks in system design, it is important to understand trends affecting premise plumbing safety.

A Perfect Storm

Both internal and external factors are contributing to the increase of Legionnaires’ disease cases in the United States. 

Aging water service infrastructure. Each year approximately 240,000 water main breaks occur in the United States (https://bit.ly/3raGvc4). According to the American Water Works Association (AWWA), repairing and replacing old water pipes could cost more than $1 trillion over the next 20 years (https://bit.ly/3IM46pf). The residual effects of water main breaks include bacterial contamination and bacterial corrosion resulting in a habitat favorable to the proliferation of waterborne pathogens. Until new infrastructure is installed, the United States will continue to experience water contamination in municipal water service and premise plumbing systems.

Wide spread use of low flow fixtures. Water use has changed drastically since the implementation of the U.S. Energy Policy Act (1992). This policy made the production and sale of low flow plumbing fixtures necessary to reduce water use; however, industry standard sizing methods for water distribution piping did not change. As a result, potable water service and water distribution systems are grossly oversized, creating an environment conducive for biofilm and bacteria growth.

Building water systems during COVID-19. Feeding the perfect storm is the extended vacancy and reduced occupancy that buildings are experiencing during the coronavirus pandemic. Re-occupying a building with neglected water systems increases the likelihood of Legionella bacteria transmission. 

Increased lawsuits. With greater understanding of the causes of Legionella, there is an increase in allegations of negligence and liability claims. With a standard of care established in ANSI/ASHRAE Standard 188, just one Legionnaires’ disease claim could cost negligent owners millions of dollars in litigation costs and settlement claims. 

Insurance coverage. Insurance companies are fighting their liability for coverage as more lawsuits and claims are brought forward. Some insurers are limiting coverage or imposing higher deductibles if building systems are outdated (https://reut.rs/33X10zS). Others are asking customers to document how they maintain plumbing and cooling systems. This is leaving building owners exposed to great financial risks. 

Owners are not the only ones exposed to allegations of negligence or liability claims; engineers are also exposed to liability given the widespread availability of industry research and recommendations concerning design strategies to control Legionella. 

Many buildings lack a water management program. According to the CDC, 9 out of 10 Legionella outbreaks could be prevented with more effective water management (https://bit.ly/3Hb1WPE). In June 2017, the Centers for Medicare & Medicaid Services (CMS) released a memo requiring health care facilities to develop and adhere to an ANSI/ASHRAE Standard 188 compliant water management program to reduce the risk for Legionella in their water systems. While this requirement was a great first step to improving public health and safety, it should not stop here. Unfortunately, facility types outside of CMS jurisdiction are not required to develop or adhere to a water management program. Without this requirement, it makes implementing proven control strategies into a wide range of building types much more difficult.

Continuous increases in construction costs. Construction costs have increased more than 5% each year since 2017 (https://bit.ly/3rUXXAp). Architectural, engineering, and construction teams are consistently asked to evaluate options for cost savings. Unfortunately, the unrelenting pressure to cut costs makes effective design concepts and innovative products developed to manage risk constantly vulnerable to elimination from the project design. 

Managing Risks

Effectively managing risks associated with building water systems takes a commitment from everyone involved, from owners and operators to engineers and contractors. 

Managing risks must be a priority of the building owner and discussed at the very beginning of project planning. Engineers should include recommended control measures in early conceptual and schematic design documents. This ensures control measures are included in initial cost estimates and creates an opportunity to discuss the owner’s priorities concerning managing Legionella.

As the project moves through design development, engineers should focus on supporting key water management principles: 

• Maintain water temperatures outside of Legionella 

growth range.

• Prevent water stagnation.

• Ensure adequate disinfection.

• Prevent scale, corrosion, and biofilm growth.

During construction, it is critical for engineers to review construction submittals through the lenses of Legionella control and assess all cost saving proposals. Yet the continuous increase in construction costs exposes effective design strategies and innovative products to elimination from the project to save money. An owner’s commitment to managing risks is vital to the successful implementation of proven control measures.

Engineers must balance public health and safety, good engineering practice, sustainability, operational efficiency and owner requirements while also being cost conscious. 

Focus on the Fundamentals

Good engineering practice starts with fundamental Legionella control measures. These control measures often have little to no cost impact. Two of the most common control measures are maintaining water temperatures (hot and cold) outside of Legionella growth range and preventing water stagnation. 

Unfavorable temperatures and water stagnation increase the likelihood of bacteria and biofilm growth. One of the biggest challenges to maintaining water temperatures is the domestic hot water recirculation system. Without proper balancing of the recirculation system, hot water circuits further away from the heat source (i.e., water heater) will struggle to meet or maintain design temperature while the hot water circuits closest to the heat source consistently maintain design temperature. 

The reason is due to water taking the path of least resistance. To balance a system, valves are installed on each hot water return circuit to create resistance. This resistance encourages water to choose an alternate path while still allowing enough flow through the circuit to overcome heat loss. A properly balanced system will maintain and deliver hot water quickly and consistently throughout the building.

Multiple issues can affect the proper balancing of a system: system design, valve selection, commissioning, scale, renovations, repairs or neglected maintenance. The bottom line is most recirculation systems do not work correctly. As such, we have multiple balancing valve technologies on the market designed to improve system balancing. 

Automated balancing valves are the best option to ensure a building consistently maintains hot water temperatures throughout the system. They provide a perfectly balanced system based on custom parameters, automate weekly maintenance to prevent scale build-up, monitor temperatures in real-time at each return circuit, and continuously log data for verification, risk assessment, and compliance.

Eliminating the potential for water stagnation using system design alone is not possible. However, engineers can reduce the potential for stagnation and support regular water exchange by using good engineering practices and manufactured solutions. Consider pipe routing, fixtures, and fittings to minimize dead legs and eliminate dead ends. In addition, provide a means to facilitate remedial or routine flushing. Routine flushing is a preventative action performed during periods of low water use or at seldom-used bypasses, mains, branches and outlets.

An overlooked potential for stagnation and bacteria growth is the period between substantial completion and building occupancy. Engineers can address stagnation during this time by including an automated system designed to periodically flush mains and branches according to time, temperature or usage. This ensures regular water exchange while the building is still unoccupied, thus minimizing bacteria and biofilm growth while maintaining residual disinfectant levels.

Minimizing and Managing Transmission 

Legionella is transmitted through aerosolization. Contaminated droplets of water enter the lungs where the bacteria can grow potentially leading to severe pneumonia. 

In building water systems, aerosolization can take place at showers, faucets, decorative fountains, cooling towers, humidifiers, etc. Engineers should consider selecting plumbing fixtures that minimize the potential of producing aerosols.

Sediment, scale, and corrosion provide a habitat and nutrients for Legionella. It is important to address these issues through the thoughtful selection of equipment and piping materials:

• Water filtration removes sediment and provides 

nutrient control.

• Water conditioning reduces scale in facilities 

with hard water.

• Supplemental disinfection allows facilities to control 

residual disinfectant levels.

• Select piping material that is corrosion-free and 

immune to degradation due to chlorine, monochlora

mine, or chlorine dioxide disinfectants.

Plumbing systems often lack the control and monitoring capabilities necessary for effective water management — even in the newest and most critical facilities. If controls and monitoring are installed, they almost exclusively require manual oversight and operation, which relies heavily on the operator's time, diligence, and expertise. 

Engineers must consider designing smarter, more intelligent systems that take advantage of market innovations to simplify water management. These systems automate fundamental control measures and allow operators to quickly respond to potentially hazardous system changes, perform risk assessments, and verify compliance with an established water management program. 

Comprehensive Plumbing Design 

Two long-term care facilities in the Southwest United States wanted to manage the risk of Legionella without the use of continuous supplemental disinfectant treatment. Engineers provided a comprehensive plumbing design by implementing a multi-barrier approach: 

• Applied control measures at the point of source including water conditioning to reduce scale, ultrafiltration for nutrient control, and UV disinfection to destroy harmful
microorganisms.

• Selected a booster pump with no accumulator tank and a flow-through expansion tank at the water heater to reduce potential risk.

• Designed hot water storage and distribution temperatures outside of Legionella growth range.

• Selected CPVC piping for hot and cold water distribution.

• Utilized “flow splitters” in the cold water system, minimizing dead legs.

• Recirculated hot water close to the fixtures to minimize the opportunity for bacteria growth and survival.

• Provided an intelligent system capable of automatically flushing valves to ensure regular water exchange, monitoring of control limits and continuous data logging.

• Provided ports for temporary supplemental disinfection (remedial or routine).

By making a conscious decision to incorporate fundamental principles and comprehensive strategies into the design process, engineers can minimize the impact of emerging trends and give building operators the systems they need to manage risks successfully.

Greg Swafford, CPD, GPD, is Technical Sales Manager, Commercial Water, for GF Piping Systems (GF). In addition to his work with GF, he serves as Affiliate Liaison for Region 5 of the American Society of Plumbing Engineers and is a committee member of ASHRAE SPC 514 “Risk Management for Building Water Systems: Physical, Chemical and Microbial Hazards.” Prior to joining GF, he was a plumbing designer, project manager, and plumbing department leader at MEP consulting firms for nearly 20 years. Contact Greg at: greg.swafford@georgfischer.com

A version of this article originally appeared in WQL.