Legionella Water Treatment Systems & Prevention Guide

Among the most daunting threats hiding within your building’s commercial plumbing system is a bacterium called Legionella pneumophila. This naturally occurring bacterium is responsible for potentially fatal respiratory illnesses, and it’s on the rise. Unfortunately, it thrives exactly where modern facilities operate: in warm, complex, and haphazardly treated water systems.

You might be surprised to learn just how common and costly this problem has become. According to a 2024 study by Kunz et al., the statistics surrounding Legionella in the United States are staggering:

• A Leading Threat: Between 2015 and 2020, Legionella was the leading cause of reported drinking water outbreaks in the U.S., accounting for 98% of all biofilm-related outbreak reports.
• An Economic Burden: Drinking water exposures linked to biofilm pathogens, primarily Legionella, cost the United States an estimated 1.39 billion dollars annually.
• Severe Health Impacts: During that same five-year period, Legionella-associated drinking water outbreaks were responsible for 544 hospitalizations and 86 deaths.

Despite these high numbers, we see many facility managers still relying on a reactive approach to water safety as opposed to a proactive water treatment system. Dumping chemical disinfectants into your system is not enough to solve the problem. The science proves that without proper physical water conditioning in the form of water softening, filtration, and reverse osmosis (RO), your chemical treatments can’t do their job.

In this guide, we’ll walk you through exactly what Legionella is, how it infiltrates your water supply, which facilities are most at risk, and how implementing custom Legionella water treatment systems can act as your ultimate first line of defense.

What is Legionella?

Legionella is a genus of pathogenic bacteria found naturally in freshwater environments like lakes, rivers, and streams. Out in nature, these bacteria exist in relatively low numbers. The natural environment is vast, and the temperatures are generally too cool for the bacteria to rapidly multiply to dangerous concentrations.

However, the situation changes when these bacteria enter your human-made water systems. Your commercial plumbing, cooling towers, boiler feeds, and water heaters provide the perfect artificial habitat for the bacteria to flourish.

Legionella loves commercial water systems because it requires three specific conditions to thrive:

• Warm Temperatures: The bacteria multiply rapidly in water sitting between 77 and 113 degrees Fahrenheit — common temperatures for hospitals, hotels, and manufacturing facilities.
• Stagnation: Water that sits in unused pipes or empty rooms loses its chemical disinfectants quickly.
• A Place to Hide: The bacteria need scale, sediment, and complex microorganisms to form a slimy protective layer known as biofilm.

This biofilm is the ultimate fortress. It protects the Legionella bacteria from extreme temperatures and expensive chemical disinfectants, rendering them ineffective.

What is Legionnaires’ Disease?

When Legionella bacteria multiply in your commercial water system, they do not spread from person to person. Instead, people are infected by inhaling microscopic water droplets, or aerosols, that contain the bacteria.

That’s right. You do not need to drink the water to contract Legionnaires’ Disease. You, your staff, and your clientele can inadvertently inhale it.

Once inhaled, the bacteria travel directly into the lungs and can cause one of two illnesses, collectively known as legionellosis. The milder form is Pontiac fever. This resembles a standard case of the flu and typically resolves on its own without medical intervention.

The severe form is Legionnaires’ disease, which is a very serious and potentially fatal type of pneumonia. If someone in your building contracts this disease, they may experience:

• Dangerously high fevers
• Severe, persistent coughing
• Shortness of breath and chest pain
• Muscle aches and severe headaches
• Gastrointestinal issues

Because these symptoms are nearly identical to other forms of pneumonia, the disease often goes undiagnosed until severe complications arise. The risk of death is significant, especially among older adults, smokers, and people with weakened immune systems. When an outbreak occurs in a vulnerable setting like a healthcare facility or nursing home, the fatality rate can reach 10% or higher.

How Does Legionella Get Into Your Water Supply?

The journey of Legionella from a municipal water source to a human lung involves a chain of environmental failures. Municipal water treatment plants do a fantastic job of sanitizing water before it leaves their facilities. But municipal water has a long way to travel. By the time it navigates miles of city infrastructure and reaches your commercial building, the residual disinfectant levels have often degraded significantly.

Once the municipal water enters your building, it brings trace amounts of Legionella along with naturally occurring minerals, specifically calcium and magnesium. These minerals are the building blocks of hard water. As this hard water runs through your commercial boilers, pipes, and heat exchangers, the calcium and magnesium precipitate out and form scale on the internal surfaces of your plumbing.

This scale is rough and highly porous. It acts as an anchor point for dirt, organic matter, and other bacteria. Together, these elements form biofilm. Deep within this biological slime, Legionella bacteria embed themselves and are consumed by single-celled organisms called amoebae. In a cruel twist of nature, instead of being digested, the Legionella bacteria multiply exponentially inside the amoebae.

When the biofilm eventually ruptures, or when water flow in your building changes abruptly, large amounts of Legionella are released into your flowing water. If this water is then aerosolized by a showerhead in your hotel, a decorative fountain in your lobby, or a cooling tower on your roof, it becomes a severe inhalation hazard for anyone nearby.

What Businesses Are Most at Risk and Why?

Not all commercial facilities face the same level of risk. The likelihood of an outbreak in your building depends heavily on the complexity of your water system, the presence of aerosolizing equipment, and the vulnerability of the people walking through your doors.

Legionella in Healthcare Facilities and Hospitals

If you manage a hospital or a long term care facility, you are operating in the highest risk environment for Legionnaires’ disease. Your buildings typically have incredibly complex plumbing networks with long runs of pipe, unused branches, and dead legs where water can sit stagnant for weeks.

Stagnant water quickly loses any remaining chemical disinfectants and drops right into the ideal temperature range for bacterial growth. Furthermore, your patient population is highly immunocompromised. Even a minute concentration of aerosolized Legionella from a patient room showerhead can trigger a deadly outbreak.

Healthcare water treatment systems for hospitals, pharmaceutical labs, and nursing homes that employ water softening, filtration, and RO systems stop Legionella at the source.

Hotels and Hospitality

The hospitality industry is notorious for Legionella outbreaks due to the extensive use of recreational water features and a lack of investment in proper hotel water treatment solutions. If you run a hotel or resort, you likely rely on elaborate pools, spas, decorative indoor fountains, and large hot water storage tanks to keep your guests comfortable.

According to a 2021 study by Hlavsa et al., between 2015 and 2019, 65 outbreaks tied to treated recreational water were caused by Legionella, resulting in 13 deaths. Strikingly, 72% of the Legionella outbreaks with a confirmed cause at hotels and resorts were associated with hot tubs. When your hotel occupancy fluctuates in the off-season, water sits stagnant in empty rooms. This leads to a massive spike in bacterial growth that is ready to strike when your next guest turns on the faucet.

Industrial Plants and Manufacturing Facilities

Industrial facilities often use large amounts of water for production and temperature regulation. While manufacturing water treatment doesn’t always involve drinking-water-level purification, your air could still transmit the bacteria via your equipment. If you manage a plant, your primary threat is likely the presence of industrial cooling towers.

Cooling towers operate by evaporating large volumes of warm water to reject heat into the atmosphere. This evaporation process creates immense plumes of water vapor that can travel for miles. If your industrial cooling tower is colonized by Legionella, that single source can infect your plant workers and even residential neighborhoods downwind.

Learn more about your cooling tower water treatment options.

The Root Cause of Outbreaks in Commercial Systems

Why do these outbreaks happen so frequently if we know how to treat water? The CDC has tracked the root causes of Legionnaires’ disease outbreaks and found that the vast majority stem from preventable maintenance and treatment gaps.

In a comprehensive review of outbreaks by Garrison et al. in 2016, researchers found that 85% of investigations revealed at least one deficiency in building water maintenance. Specifically, the failures broke down as follows:

• 65% were linked to process failures, such as inadequate water treatment.
• 52% were linked to human errors.
• 35% were linked to equipment failures.

You might be making the common mistake of viewing water treatment solely as the application of chemical biocides. However, chemical disinfectants cannot penetrate thick scale or layers of sediment. If your water system is choked with hard water deposits, you are accidentally providing the bacteria with a bomb shelter. The chemicals wash over the scale, leaving the Legionella safe and thriving underneath.

Legionella in Boilers and Cooling Towers

To truly protect your facility, you must look closely at your most vulnerable equipment: your boilers and cooling towers.

Boilers are responsible for heating water for your entire facility. Because calcium and magnesium precipitate out of water faster at higher temperatures, your commercial boilers are prime targets for extreme scale buildup. A scaled boiler is not just highly inefficient and costly to operate; it also creates a large surface area for biofilm development. As water moves from your boiler through the distribution system, any drop in temperature allows the bacteria nested in that scale to multiply. That’s why a water softener for your boiler feed is essential.

Cooling towers represent an even greater challenge. Because they evaporate water to release heat, the remaining water left in your tower becomes concentrated with minerals and airborne contaminants. This concentrated, warm, oxygen-rich water is the perfect biological incubator. A 2015 study by Li et al. analyzed industrial cooling tower environments and found that 26.4% of untreated water samples tested positive for Legionella, reaching dangerous concentrations as high as 1,500 CFU per liter.

Research clearly indicates that shock treatments and continuous disinfection are necessary, but they are insufficient on their own. As noted by Iervolino et al. in 2017, environmental monitoring, physical filtration, and anti-scale treatments must be deployed together to ensure good system performance and meaningfully reduce public health risks.

How You Can Prevent Legionella Using Physical Water Treatment Systems

The secret to proper commercial water management is the multi-barrier approach. Instead of reactively trying to kill the bacteria once they have already colonized your pipes, your goal should be to systematically remove their habitat, which is scale. Using a system that strips the water of the minerals, sediment, and organics that the bacteria rely on to survive allows you to render your facility virtually inhospitable to Legionella.

Commercial Water Softeners: Eliminating the Habitat

The first line of defense in your water management plan should be a commercial water softener. Commercial softeners use an ion exchange process to physically remove the problematic calcium and magnesium ions from your incoming municipal water supply, replacing them with harmless sodium ions.

By eliminating the hardness minerals, you stop the formation of scale inside your boilers, pipes, cooling towers, and heat exchangers. Without scale, the internal surfaces of your plumbing remain smooth and clean. Biofilm has nothing to anchor onto, and Legionella loses its physical shield. When your water is soft, the standard chemical disinfectants you already use finally have the ability to work at maximum efficiency, easily reaching and neutralizing any free-floating bacteria.

Commercial Water Filtration Systems: Physical Removal

While softeners handle dissolved minerals, you must also address physically suspended solids. Municipal water often carries silt, sand, rust, and organic matter into your building. These particles accumulate in the bottom of your hot water storage tanks and cooling tower basins, creating a sludge that serves as an all-you-can-eat buffet for bacteria.

Our custom commercial water filtration systems physically trap and remove these suspended solids before they can settle in your infrastructure. We can also customize advanced media filters to remove iron and manganese, two elements that certain types of bacteria specifically feed upon. Use physical water treatment systems to filter out the physical debris and organic food sources, and you effectively starve the biofilm and stop Legionella colonization before it starts.

Reverse Osmosis (RO) Systems: For Medical-Grade Purity

For facilities that require the highest possible standard of water purity, such as healthcare applications, pharmaceutical manufacturing, or high tech industrial processes, commercial Reverse Osmosis (RO) systems are the ultimate solution.

Commercial RO systems force water under high pressure through a semipermeable membrane. This membrane is so fine that it strips away up to 99% of all dissolved solids, contaminants, and impurities. RO systems provide practically pure makeup water for your most sensitive equipment. When you feed a high-pressure boiler or an advanced cooling process with RO water, you eliminate the variables of incoming water quality. Furthermore, when combined with our specialized PFAS removal systems, we protect your facility not just from biological threats like Legionella, but from emerging chemical contaminants as well.

Customizing the Best Legionella Water Treatment Solution for Your Facility

We know that no two commercial buildings are exactly alike. The water chemistry, flow rates, plumbing architecture, and daily demands of a high rise hotel are vastly different from those of an industrial manufacturing plant. Implementing an effective water treatment strategy requires a tailored approach.

We do not believe in off the shelf solutions because they rarely provide the protection required for true Legionella prevention. A system that is too small will cause unacceptable pressure drops in your building and fail to condition the water properly during peak usage hours. A system that is too large can cause water channeling and stagnation within the resin beds.

A thorough site survey and water quality analysis are our mandatory first steps. We test your incoming water for hardness, pH, total dissolved solids, iron content, and chlorine levels so our engineers can design a system that precisely matches your facility’s specific risk profile. We customize the footprint, resin capacity, and control valves to ensure that your water softening and filtration systems operate seamlessly behind the scenes, protecting your building 24 hours a day.

Secure Your Legionella Water Treatment System with Hill

Legionella is a complex, resilient, and deadly threat to your commercial facility, but outbreaks are entirely preventable. Trusting chemical disinfectants alone is a gamble that you can no longer afford to take. By preventing scale, removing sediment, and starving biofilm, you can permanently dismantle the environment that allows Legionella to thrive.

Don’t wait for a positive Legionella test or a localized outbreak to evaluate your water infrastructure. Take control of your building’s water quality today.

We invite you to reach out to the commercial water treatment experts at Hill to learn more about our custom water softeners, advanced filtration, reverse osmosis, and PFAS removal systems. Let our team of specialists customize the perfect solution to keep your facility safe, compliant, and scale-free.