Controlling Legionella in water systems: Chemical disinfection vs. certified ultrafiltration

According to the CDC, no single control measure, including chemical disinfection, can ensure Legionella elimination.

Legionella can persist within biofilms, sediment, and stagnant piping zones, where disinfectant residuals fail to reach. The CDC further cautions that even chemical shock or supplemental disinfection systems cannot provide lasting control without a comprehensive water management plan (WMP).

That’s why the CDC recommends layered protection for controlling Legionella in water systems, combining chemical disinfection with certified point-of-use ultrafiltration to achieve reliable, continuous control.

How does Legionella grow inside the plumbing system?

Legionella thrives in areas of plumbing systems where water flow is irregular or stagnant. These bacteria often colonize dead legs, low-flow outlets, thermostatic mixing valves, storage tanks, and aging pipework, where temperatures fluctuate and disinfectant levels drop. 

Over time, biofilm layers form on pipe walls, providing a protective environment that shields bacteria from heat and chemicals. For installers & plumbers, stagnation zones and poor temperature balance become high-risk points for contamination. 

In healthcare facilities, dental clinics, and hotels, where water systems are complex and usage varies, these hidden growth areas can quickly compromise safety.

Understanding these conditions allows plumbers & installers to design, maintain, and retrofit systems that minimize bacterial risk and ensure effective waterborne bacteria removal.

What are the advantages and disadvantages of chemical disinfection?

Chemical disinfection remains a widely used method for Legionella control in water systems, particularly for short-term remediation or shock treatment.

Advantages of chemical disinfection

• Effective for immediate remediation: Useful for shock treatment during Legionella contamination events.

• System-wide reach: Can be applied through existing plumbing infrastructure to treat large water systems.

• Relatively simple setup: Requires minimal mechanical changes compared to filtration or redesign.

• Recognized control measure: Commonly included in water management plans for compliance purposes.

Disadvantages of chemical disinfection

• Ineffective against biofilm: Disinfectants often cannot penetrate biofilm, where Legionella hides and multiplies.

• pH and temperature sensitivity: Chemical disinfectants rely on maintaining a specific pH balance, which even slight temperature changes can disrupt.

• Limited reach: Effectiveness decreases in complex piping or at distal outlets with stagnant water.

• Potential system damage: Prolonged chemical use may cause corrosion, scaling, or material degradation.

• Ongoing maintenance: Requires continuous monitoring, dosing, and safe storage of chemicals.

• Not ideal for sensitive environments: Chemical residues may pose risks in healthcare or dental settings.

Certified ultrafiltration: Preventing Legionella at the source

Mentor Water Technology certified ultrafiltration provides a physical barrier that prevents Legionella and other microbes from reaching outlets. While various water treatment systems, such as UV disinfection, copper-silver ionization, or chemical dosing, may also carry certifications, they work through inactivation or chemical processes rather than physical retention.

MWT filters are equipped with advanced ultrafiltration membranes with a pore size of 0.08 µm, delivering consistent microbial protection even when water temperature or chemistry fluctuates.

Our certified point-of-use (POU) and point-of-entry (POE) filters meet stringent standards such as ASHRAE 188, EPA WaterSense, ASTM, ASSE, and NSF/ANSI, helping installers and plumbers maintain full water safety compliance. 

In healthcare facilities, hotels, and dental clinics, installing certified ultrafiltration at outlets provides real-time protection against waterborne bacteria, safeguarding patients, staff, and guests while ensuring systems remain compliant, reliable, and easy to maintain.

The smart control strategy- Certified ultrafiltration

While chemical disinfection helps manage overall water quality, it cannot guarantee complete protection at every outlet. Certified ultrafiltration provides that final layer of defense, preventing Legionella and other pathogens before they reach the user. 

By combining certified technologies with proper installation practices, plumbers and installers can create water systems that remain Legionella-proof, ensuring both client safety and regulatory compliance.

MWT-Direct helps professionals get it right from the start. Every MWT filter is produced in an EPA FIFRA-registered establishment (No. 105402-NLD-1) and independently tested under ASTM F838-2020, ASSE 2011-2022, EPA WaterSense, and NSF standards. 

With Log 8 (99.999999%) bacterial reduction efficiency, zero water waste, and extended product life, MWT filters deliver reliable protection, available direct to installers, with no minimum orders and fast U.S. delivery.

Protect your next installation with certified, U.S.-tested filters. Buy Legionella protection filters on MWT-Direct: https://www.mwt-direct.com