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Legionella in water systems- What every plumber & installer must know?



For plumbers and installers, this highlights the critical role they play in protecting water systems. Legionella spreads through (cold & warm), stagnant water and an outlet, like a shower or tap, to aerosolize. 


Understanding how Legionella in water systems thrives, where risks hide in plumbing, and which certified solutions help prevent it is essential. What might seem like a minor design oversight or maintenance gap can quickly escalate into a health crisis, regulatory action, or costly shutdown for a facility.


What is Legionella?

Legionella is a type of bacteria that causes Legionnaires’ disease, a severe form of pneumonia, and Pontiac fever, a flu-like illness. 


Several conditions can create the perfect environment for Legionella to multiply in water systems:

  • Biofilm buildup, slimy layers inside pipes that harbor bacteria.

  • Warm temperatures, especially between ≥ 68°F ≤122°F, are ideal for growth.

  • Low disinfectant levels, insufficient chlorine, or other residuals that normally keep bacteria in check.

  • Stagnant water, slow flow, or unused outlets that allow microorganisms to grow.


High-risk environments include hospitals, nursing homes, hotels, gyms, sports complexes, and apartments with communal showers.


How does Legionella spread in water systems?

Legionella becomes dangerous when water carrying the bacteria turns into tiny airborne droplets that people can inhale. This happens through everyday fixtures like 

  • Showers

  • Faucets

  • Cooling towers

  • Whirlpools

  • Decorative fountains

  • Dental units


Breathing in these tiny droplets can lead to Legionnaires’ disease or Pontiac fever. Risks not only come from stagnant water sitting in pipes, where warm temperatures and biofilm support bacterial growth.


Contaminated water can also enter from the municipal supply, wells, or a facility’s own pipeline system, creating multiple pathways for Legionella to spread.


When a tap or shower is opened, those bacteria can be released into the air. For plumbers and installers, this makes aerosolization a critical concern, making a hidden water issue into a serious airborne health risk.


What are the best practices for plumbers and installers to prevent Legionella?

Protecting clients requires a balance of good system design, a water management program, and certified technology. Some key practices include:

  • Temperature control: Store hot water at ≥(165 °F) and deliver it at (122 °F). Keep cold water below ≤ (63 °F).

  • System flushing: Flush unused outlets weekly to reduce stagnation.

  • Design with safety: Avoid dead legs and oversized tanks. Use pipework materials that resist scale buildup.

  • Testing: Apply a water management program and water testing every quarter.

  • Filtration where it matters most: Install certified ultrafiltration at the POU, such as taps and showers.

  • Follow compliance standards: ASHRAE guidance, including Chapter 12, Standard 188, and Standard 514 and local health regulations.


How can certified filtration solutions help prevent waterborne risks?

Standard disinfection alone is not always enough. Legionella can survive within biofilms and recolonize quickly after treatment. Certified filtration is now a vital layer of defense in water safety.


MWT’s solutions, including hollow-fibre ultrafiltration membranes with a 0.08 μm pore size, are tested to achieve Log 8 (99.999999%) bacterial reduction against Legionella pneumophila, Pseudomonas, NTM, and other pathogens.


Mentor Water’s products are certified by IAPMO for NSF, ASSE, and U.S. EPA Pesticide Reduction, and have been tested in accordance with ASHRAE performance criteria. 


They also comply with European safety and regulatory standards, including the EU Drinking Water Directive (2020/2184) and DIN EN 16421, reflecting our commitment to global excellence. For plumbers and installers, choosing products with certifications ensures both safety and compliance. 


Certified water filters- Delivered direct to plumbers & installers

MWT-Direct lets plumbers and installers buy Mentor Water Technologies certified water filters directly, making professional-grade water safety easier than ever. 


Every product is certified and tested in the USA, produced in an EPA FIFRA-registered establishment (No. 105402-NLD-1), and proven to reduce Legionella, NTM, and other harmful waterborne bacteria. Get rapid U.S. delivery with no minimum order requirements.


Explore MWT’s certified filters today and protect every installation: https://www.mwt-direct.com/

 
 
 

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