How to prevent Legionella in water systems: 5 common mistakes to avoid

Plumbers and installers play a crucial role in protecting building occupants from waterborne pathogens, such as Legionella, the bacterium responsible for Legionnaires’ disease.

Even well-designed plumbing systems can become breeding grounds for Legionella if installation and maintenance practices overlook key details.

Here are 5 common mistakes that compromise water safety and how to prevent Legionella in water systems using industry best practices and certified filtration systems.

Mistake #1: Ignoring water stagnation zones

Stagnant water is one of the leading causes of Legionella growth. When water sits idle in dead legs, unused outlets, or oversized pipes, it warms up and loses disinfectant residuals, creating ideal conditions for bacterial colonization.

How to avoid it:

• Keep pipe runs as short as possible and eliminate dead ends.

• Use recirculating loops or timed flushing to maintain flow through rarely used outlets.

• If fixtures remain unused, flush them weekly to refresh the water and maintain disinfectant levels.

A well-designed circulation plan keeps water moving, the simplest and most effective defense against stagnation-related contamination.

Mistake #2: Poor temperature control

Legionella bacteria thrive in water temperatures between 68°F and 122°F. Systems that allow water to stay within this range, particularly in storage tanks or recirculation loops, provide the perfect environment for growth.

How to avoid it:

• Keep hot water above 140°F and cold water below 68°F.

• Prevent unwanted heat transfer between hot and cold pipes.

• Install temperature sensors at multiple points in the system to ensure compliance.

Stable temperatures significantly reduce the risk of bacterial amplification and are essential to any Legionella prevention plan.

Mistake #3: Neglecting proper cleaning and maintenance

Sediment, scale, and biofilm act as both a food source and a shield for Legionella, protecting it from chemical disinfectants and allowing colonies to persist deep inside plumbing systems.

How to avoid it:

• Establish and follow a regular cleaning and disinfection schedule for all water-related components, especially those generating aerosols.

• Clean and descale showerheads, hoses, and aerators to remove mineral buildup where bacteria can thrive.

• Periodically inspect water storage tanks for corrosion, sediment, or debris, and ensure tight-sealing covers to prevent contamination.

Consistent maintenance is about compliance, reliability, and safety for everyone using the water.

Mistake #4: Relying solely on chemical treatments

Chemical disinfectants like chlorine or monochloramine play a valuable role in controlling microbial growth. However, when used alone, they often fail to remove bacteria embedded within biofilms or stagnant areas.

The efficacy of chemical disinfectants depends on maintaining a stable pH balance, which can be affected by minor fluctuations in temperature.

How to avoid it:

• Combine chemical disinfection with physical control methods such as system flushing, temperature management, and certified filtration.

• Check disinfectant residuals across the system to ensure they reach distal outlets,  and use pH balance sensors to verify that disinfectant effectiveness is maintained throughout the system.

• Consider complementary technologies like ultrafiltration for comprehensive Legionella control.

Remember, chemicals can treat water, but certified filtration reduces pathogens before they exit the outlet. 

Mistake #5: Using uncertified filters or devices

Installing filters without verified certification under NSF, ASSE, or ASTM standards, or from non-registered establishments, doesn’t reduce pathogens like Legionella or NTM.

How to avoid it:

• Always choose filters independently tested under NSF, ASSE, or ASTM standards.

• Ensure filters are produced in EPA FIFRA-registered establishments for verified antimicrobial performance.

• Keep certification records for audits, especially when serving healthcare or hospitality clients.

For true end-user safety, Point-of-Use (POU) filters with active barrier filtration are the most reliable solution. They reduce waterborne pathogens at the outlet, preventing contamination even if upstream systems fail.

POU filters can work independently or complement a Point-of-Entry (POE) system, providing layered, certified protection against Legionella and other microbes.

Get certified filters for Legionella prevention on MWT-Direct

Legionella prevention starts with installation, and MWT-Direct helps you get it right from the start. Every MWT filter is produced in an EPA FIFRA-registered establishment (No. 105402-NLD-1) and independently tested to meet the highest global standards, including ASTM F838-2020 for Log 8 (99.999999%) bacterial reduction, ASSE 2011-2022 for plumbing performance, and EPA WaterSense for water efficiency.

MWT-Direct delivers certified, professional-grade filtration solutions direct to plumbers and installers across the U.S., and trusted Legionella protection in every system.

Buy Certified Filters at MWT-Direct: https://www.mwt-direct.com/