Legionella Control Using Chlorine Dioxide: A Modern Approach to Building Water Safety

Introduction

Legionella remains one of the most significant water hygiene challenges facing building owners, facilities managers, healthcare providers, hotels, holiday parks and commercial property operators throughout the United Kingdom.

Every year, organisations invest substantial resources into monitoring, testing and managing water systems to reduce the risk of Legionella bacteria colonising pipework, storage tanks and outlets.

While traditional control measures continue to play an important role, increasing attention is being given to chlorine dioxide as a highly effective tool for Legionella control and biofilm management.

This article explores how Legionella develops within building water systems, why biofilm plays a critical role in bacterial survival and how chlorine dioxide is increasingly being used as part of comprehensive water hygiene programmes.

What Is Legionella?

Legionella is a naturally occurring bacterium found in freshwater environments.

Under normal environmental conditions, Legionella exists at low concentrations and presents minimal risk.

Problems arise when the bacteria enter man-made water systems where conditions allow multiplication.

Examples include:

• Cold water storage tanks
• Hot water systems
• Pipework networks
• Dead legs
• Showers
• Cooling towers
• Decorative water features
• Spa pools
• Healthcare water systems

When contaminated water becomes aerosolised, individuals may inhale droplets containing Legionella bacteria.

In susceptible individuals this can result in Legionnaires' disease, a potentially serious form of pneumonia.

Why Legionella Remains a Major Concern

Legionnaires' disease continues to be one of the most closely monitored waterborne illnesses within the UK.

Particular concern exists within:

• Hospitals
• Care homes
• Hotels
• Holiday parks
• Schools
• Universities
• Commercial buildings
• Leisure facilities

The consequences of inadequate water hygiene management can include:

• Illness
• Regulatory investigations
• Civil claims
• Reputational damage
• Remedial costs
• Building closures

For this reason, effective Legionella control remains a key component of water management programmes.

Understanding Legionella Growth Conditions

Legionella does not simply appear within water systems.

It requires conditions that support survival and multiplication.

Common contributing factors include:

Stagnation

Water that remains static for extended periods provides ideal conditions for microbial growth.

Examples include:

• Unused outlets
• Dead legs
• Infrequently used rooms
• Seasonal accommodation

Temperature

Legionella grows most effectively between approximately 20°C and 45°C.

Poor temperature control can therefore significantly increase risk.

Scale and Sediment

Mineral deposits provide surfaces on which microorganisms can attach and multiply.

Biofilm

Perhaps the most important factor of all is biofilm.

What Is Biofilm?

Biofilm is a layer of microorganisms that attaches to internal pipe surfaces.

Within a biofilm, bacteria become embedded in a protective matrix.

This matrix can shield microorganisms from:

• Disinfectants
• Water flow
• Environmental changes

Biofilm may contain:

• Legionella
• Pseudomonas
• E. coli
• General bacterial populations
• Fungi
• Algae

Once established, biofilm can become extremely difficult to remove.

Many recurring Legionella problems are linked directly to biofilm development.

Why Biofilm Matters

Traditional water treatment approaches often focus on achieving disinfectant residuals.

However, a disinfectant residual alone may not eliminate microorganisms protected within biofilm.

This means that:

• Water samples may appear satisfactory.
• Hidden contamination may still exist.
• Bacteria may recolonise the system over time.

Modern water hygiene programmes increasingly focus on managing both free-floating microorganisms and the biofilm structures that support them.

Traditional Legionella Control Methods

Water hygiene professionals typically employ multiple control measures simultaneously.

These may include:

Temperature Control

Maintaining:

• Cold water below 20°C
• Hot water above 50°C

can significantly reduce Legionella growth.

System Design

Reducing stagnation by:

• Removing dead legs
• Improving circulation
• Encouraging regular use

helps minimise risk.

Flushing Programmes

Routine flushing reduces water age and discourages stagnation.

Chlorination

Chlorine-based disinfection remains widely used throughout the water industry.

While effective, chlorination may face challenges when biofilm becomes established.

What Is Chlorine Dioxide?

Chlorine dioxide is a powerful oxidising disinfectant used extensively in water treatment applications worldwide.

Unlike chlorine, chlorine dioxide:

• Remains dissolved as a gas in solution
• Maintains effectiveness across a broad pH range
• Produces fewer chlorinated organic by-products
• Demonstrates excellent biofilm penetration

These characteristics have made chlorine dioxide increasingly attractive for Legionella control programmes.

How Chlorine Dioxide Works

Chlorine dioxide acts through oxidation.

Rather than chlorinating contaminants, chlorine dioxide selectively oxidises cellular components that are essential for microbial survival.

This process can:

• Damage bacterial cell walls
• Disrupt metabolic processes
• Inactivate microorganisms
• Penetrate biofilm structures

The result is highly effective microbiological control across a wide range of water treatment applications.

Chlorine Dioxide and Biofilm Control

One of the most widely recognised advantages of chlorine dioxide is its ability to penetrate biofilm.

Where biofilm exists:

• Legionella may be protected.
• Pseudomonas may be protected.
• Microbial regrowth may occur.

Chlorine dioxide can diffuse into these structures more effectively than many conventional disinfectants.

Potential benefits include:

• Improved biofilm disruption
• Reduced bacterial sheltering
• Enhanced system cleanliness
• Improved long-term control

For many water hygiene professionals, biofilm management is one of the strongest reasons for selecting chlorine dioxide.

Chlorine Dioxide vs Chlorine for Legionella Control

Biofilm Penetration

Chlorine Dioxide

Excellent

Chlorine

Moderate

pH Dependence

Chlorine Dioxide

Minimal

Chlorine

Significant

As pH increases, chlorine efficiency can reduce.

Chlorine dioxide maintains more consistent performance.

By-Product Formation

Chlorine Dioxide

Generally lower formation of chlorinated organic compounds.

Chlorine

Can generate higher levels of chlorinated by-products when reacting with organic contamination.

Odour

Chlorine Dioxide

Low odour.

Chlorine

More noticeable chlorine smell.

Long-Term Water Hygiene Programmes

Chlorine Dioxide

Frequently used for ongoing Legionella management.

Chlorine

Frequently used for shock disinfection and commissioning.

Where Chlorine Dioxide Is Commonly Used

Chlorine dioxide is frequently used in:

Hospitals

Where vulnerable individuals require enhanced protection.

Care Homes

Where Legionella risk management is critical.

Hotels

Where extensive pipework and variable occupancy can increase water age.

Holiday Parks

Where seasonal occupancy may lead to stagnation.

Educational Facilities

Where periods of low usage can occur during holidays.

Commercial Buildings

Where changing occupancy patterns affect water demand.

Example ChloroKlean Dosing Guide

The following example demonstrates approximate chlorine dioxide concentrations based on ChloroKlean dosing.

Assuming:

20 ml ChloroKlean per 1,000 litres produces approximately 0.5 ppm chlorine dioxide.

Actual residual concentrations should always be confirmed using appropriate testing procedures.

Why Hotels and Holiday Parks Are Reviewing Chlorine Dioxide

Hotels and holiday parks often face unique water hygiene challenges:

• Seasonal occupancy
• Variable water demand
• Long pipe runs
• Multiple buildings
• Infrequently used outlets

These conditions can encourage:

• Water stagnation
• Biofilm development
• Increased microbiological risk

Chlorine dioxide is increasingly being evaluated as part of strategies designed to address these challenges.

Why Healthcare Facilities Use Chlorine Dioxide

Healthcare environments often require extremely robust water hygiene controls.

Benefits commonly associated with chlorine dioxide programmes include:

• Excellent biofilm penetration
• Strong Legionella control
• Consistent performance
• Broad-spectrum microbiological activity

These characteristics have contributed to widespread adoption within healthcare water management programmes.

Building a Successful Legionella Control Strategy

No single disinfectant provides complete protection on its own.

Effective Legionella management requires:

• Risk assessments
• Temperature control
• System maintenance
• Flushing programmes
• Monitoring
• Sampling
• Biofilm management
• Appropriate disinfection

Chlorine dioxide can play an important role within this broader framework.

Conclusion

Legionella control is no longer simply about maintaining a disinfectant residual.

Modern water hygiene programmes increasingly recognise the importance of biofilm management, system design and proactive risk reduction.

Chlorine dioxide has gained significant attention because of its ability to combine strong microbiological performance with excellent biofilm penetration.

For building owners, facilities managers, hotels, care homes and healthcare providers seeking to strengthen their water hygiene programmes, chlorine dioxide offers a compelling option for improving Legionella control and supporting long-term water system safety.

ChloroKlean provides a chlorine dioxide solution designed to support modern water hygiene strategies and help organisations maintain cleaner, safer building water systems.