Legionella in plumbing and heating systems: why prevention starts with system design
When talking about Legionella, people often think about the issue only when a risk or contamination event arises.
In reality, Legionella prevention in plumbing and heating systems starts much earlier: it begins with proper system design, correct temperature management, and the selection of solutions capable of ensuring circulation, safety and long-term reliability.
In modern buildings — residential, hospitality, healthcare and industrial facilities — water systems are becoming increasingly complex. For this reason, greater attention must be paid to domestic hot water management. Today, water safety is no longer simply a maintenance issue; it has become a true system design responsibility.
What is Legionella and why can it develop in water systems?
Legionella is a bacterium naturally present in aquatic environments that can proliferate inside water systems when certain conditions occur.
Transmission mainly happens through the inhalation of contaminated aerosols, meaning microscopic water droplets generated by showers, taps or misting systems. It is not transmitted through water ingestion.
The risk increases especially when systems include:
- water stagnation
- low-use sections or “dead legs”
- biofilm and scale deposits
- temperatures favorable to bacterial growth
The most critical temperature range is between 25°C and 50°C, while the bacterium is progressively inactivated at temperatures above 55°C.
This is exactly where system design and water management make the difference.
Why water temperature is so important
One of the key aspects of Legionella prevention is the control of domestic water temperature.
In modern systems, maintaining the correct temperatures is not only essential for ensuring comfort, but also for reducing biological risk.
The most commonly adopted operating guidelines include:
- cold water below 25°C
- domestic hot water above 55°C
- periodic thermal disinfection cycles at 65–70°C
When temperature is not properly managed, conditions that favor bacterial growth increase, especially in the presence of water stagnation or insufficient recirculation.
For this reason, thermal control should be considered an integral part of system design.
Plumbing systems and Legionella: why recirculation is essential
One of the main risk factors in plumbing and heating systems is water stagnation.
Dead-end sections, low-use lines, or poorly optimized distribution layouts can create areas where water remains stagnant for extended periods, encouraging bacterial growth.
To reduce this risk, modern system design increasingly prioritizes solutions that ensure:
- continuous recirculation
- reduced unused water volumes
- elimination of “dead legs”
- more uniform temperature distribution
In this context, loop system layouts represent a particularly effective solution because they keep water continuously circulating throughout the system, reducing critical areas and improving temperature stability.
Prevention is not only about maintenance
People often assume that preventing Legionella simply means carrying out periodic treatments or sanitation procedures.
In reality, maintenance is only one part of the strategy.
A truly safe system is built on an integrated approach that includes:
- proper system design
- temperature management
- regular use of water outlets
- scheduled maintenance
- dedicated disinfection treatments when required
The quality of materials also plays a key role.
Components resistant to thermal shock and compatible with disinfection treatments help maintain long-term reliability and safety.
Anti-Legionella treatments: thermal, chemical and filtration solutions
When necessary, Legionella control can be supported through specific treatment methods.
Among the most commonly used solutions are:
- thermal treatment through heat shock cycles at 70–80°C
- continuous domestic hot water temperatures above 55°C
- controlled chemical treatments
- terminal filtration systems for showers and taps
However, each solution must be compatible with system materials and properly managed, especially in more complex or sensitive buildings such as healthcare facilities, hotels and industrial plants.
Legionella regulations: why safety is also a legal obligation
In recent years, regulatory attention on Legionella prevention has grown significantly.
In Italy, Legionella prevention is governed by specific guidelines and regulatory frameworks, including:
- Legislative Decree 81/2008
- National Guidelines 2015
- Legislative Decree 18/2023 regarding water intended for human consumption
These regulations assign specific responsibilities to building owners and system operators, who are required to assess risk, implement preventive measures, and ensure regular maintenance and monitoring.
Today, water safety is no longer an option — it is both a design and management responsibility.
