Chlorine Dioxide vs Chlorination for Water System Commissioning: Which Is Best?

Introduction

Water system commissioning is a critical stage in the construction, refurbishment and maintenance of commercial and residential buildings. Whether installing a new cold-water distribution system, replacing pipework, commissioning a hotel, opening a care home or upgrading a holiday park, disinfection of the water system is essential before it is brought into service.

For decades, chlorination using sodium hypochlorite or calcium hypochlorite has been the standard approach. Most commissioning specifications continue to reference chlorine-based disinfection procedures due to their long-established use throughout the water industry.

However, increasing attention is being given to chlorine dioxide as an alternative disinfection technology, particularly in applications where biofilm control, Legionella management and long-term water hygiene performance are priorities.

This article explores the differences between chlorine dioxide and traditional chlorination, highlighting how each technology performs in building water systems and why many water hygiene professionals are evaluating chlorine dioxide as part of their commissioning and disinfection programmes.

What Is Water System Commissioning?

Water system commissioning refers to the process of cleaning, disinfecting, testing and verifying a water system before it enters service.

Commissioning may apply to:

• New buildings
• Hotels
• Care homes
• Hospitals
• Schools
• Leisure centres
• Holiday parks
• Apartment developments
• Commercial offices
• Industrial facilities

The purpose of commissioning is to ensure that the system is microbiologically safe and suitable for supplying potable water.

During construction, pipework may become contaminated with:

• Dust
• Dirt
• Construction debris
• Organic material
• Bacteria
• Biofilm-forming microorganisms

Without proper disinfection, these contaminants can compromise water quality and increase the risk of microbial growth within the system.

Traditional Chlorination for Water System Disinfection

The most widely used commissioning method involves chlorination using sodium hypochlorite or calcium hypochlorite.

The process generally includes:

1. Filling the system.
2. Dosing chlorine into the pipework.
3. Achieving a target free chlorine concentration.
4. Maintaining contact time.
5. Flushing the system.
6. Sampling and verification.

Many specifications reference disinfection concentrations of approximately 50 ppm free chlorine with a minimum contact period of one hour.

Chlorination remains widely used because:

• Contractors understand the process.
• Testing methods are well established.
• Chlorine products are readily available.
• Industry guidance has traditionally been written around chlorine chemistry.

While chlorination is highly effective against many microorganisms, it is not without limitations.

What Is Chlorine Dioxide?

Chlorine dioxide is a powerful oxidising disinfectant used throughout the water treatment industry.

Unlike chlorine, chlorine dioxide remains dissolved as a gas in solution and does not hydrolyse significantly when introduced into water.

This gives chlorine dioxide several unique characteristics:

• Broad-spectrum microbiological activity
• Excellent biofilm penetration
• High effectiveness across a wide pH range
• Reduced formation of chlorinated organic by-products
• Strong performance against Legionella and Pseudomonas

Chlorine dioxide has been used extensively in:

• Drinking water treatment
• Healthcare facilities
• Hospitals
• Care homes
• Industrial water systems
• Food processing facilities
• Cooling towers
• Water hygiene programmes

Understanding Biofilm

One of the most important factors in water hygiene is biofilm.

Biofilm is a protective layer of microorganisms that develops on internal pipe surfaces.

Within this layer, bacteria can:

• Attach to surfaces
• Reproduce
• Exchange nutrients
• Resist disinfectants

Biofilm can protect harmful microorganisms including:

• Legionella pneumophila
• Pseudomonas aeruginosa
• E. coli
• Total viable bacterial populations

In many systems, recurring microbiological failures are linked to biofilm rather than free-floating bacteria.

This is why modern water hygiene strategies increasingly focus on biofilm management rather than simply achieving a temporary disinfectant residual.

Chlorine Dioxide and Biofilm Penetration

One of the primary advantages of chlorine dioxide is its ability to penetrate biofilm.

Unlike free chlorine, which may react rapidly with the outer layers of organic contamination, chlorine dioxide can diffuse more effectively into biofilm structures.

Potential benefits include:

• Improved biofilm disruption
• Better penetration of pipe deposits
• Enhanced access to embedded microorganisms
• Reduced potential for bacterial recolonisation

This characteristic has contributed significantly to chlorine dioxide's growing use within Legionella control programmes.

Chlorine Dioxide vs Chlorination

Effectiveness Against Legionella

Legionella remains one of the most significant water hygiene concerns for building owners.

Both chlorine and chlorine dioxide are capable of controlling Legionella when applied correctly.

However, chlorine dioxide is often selected for systems where:

• Biofilm is present
• Long pipe runs exist
• Dead legs are difficult to eliminate
• Ongoing control is required

Its ability to penetrate biofilm can provide advantages in complex systems where bacteria may be protected from conventional disinfection methods.

Effectiveness Against Pseudomonas

Pseudomonas aeruginosa presents a significant challenge in healthcare, hospitality and leisure environments.

Chlorine dioxide has demonstrated strong activity against Pseudomonas and is frequently incorporated into water management programmes where microbial control is a priority.

Performance Across Different pH Levels

Chlorine effectiveness depends heavily on pH.

As pH increases:

• The proportion of hypochlorous acid decreases.
• Disinfection efficiency can reduce.

Chlorine dioxide is significantly less affected by pH changes.

This allows more consistent performance across varying water conditions.

Corrosion Potential

High-strength chlorination can contribute to corrosion of:

• Pipework
• Valves
• Fittings
• Storage tanks

Corrosion risk depends on multiple factors, including:

• Concentration
• Contact time
• Water chemistry
• Construction materials

Many water hygiene professionals consider chlorine dioxide to present lower corrosion potential than equivalent chlorination programmes.

Odour and User Experience

Traditional chlorination often produces a strong chlorine odour.

Chlorine dioxide generally produces a much less noticeable smell.

This can be advantageous in:

• Hotels
• Care homes
• Healthcare facilities
• Commercial buildings

where occupant experience is important.

Comparing Water System Disinfection Technologies

Example Chlorine Dioxide Dosing Guide

The following example illustrates 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 verified using appropriate testing procedures.

Applications Suitable for Chlorine Dioxide

Chlorine dioxide may be considered for:

• New building commissioning
• Cold water storage tanks
• Pipework disinfection
• Legionella remediation
• Hotel water systems
• Holiday park water systems
• Care homes
• Schools
• Universities
• Healthcare facilities
• Commercial office buildings

In many cases, chlorine dioxide is selected because the objective extends beyond simple disinfection and includes long-term biofilm management.

Is Chlorine Dioxide Replacing Chlorination?

The reality is more nuanced.

Traditional chlorination remains the most widely specified commissioning method throughout the UK.

However, chlorine dioxide continues to gain attention due to its:

• Biofilm penetration capabilities
• Legionella control performance
• Reduced pH dependency
• Lower tendency to form chlorinated organic by-products
• Established use within healthcare and water hygiene sectors

Rather than replacing chlorination entirely, chlorine dioxide is increasingly being evaluated as an additional option within modern water management programmes.

Why Building Owners Are Looking Beyond Traditional Chlorination

Building owners today face increasing pressure to demonstrate effective control of:

• Legionella
• Pseudomonas
• Waterborne pathogens
• Biofilm development

As understanding of biofilm continues to evolve, many organisations are reviewing whether traditional commissioning methods alone are sufficient to support long-term water hygiene objectives.

Chlorine dioxide offers an alternative approach that combines strong microbiological performance with proven biofilm control capabilities, making it an increasingly attractive option for water hygiene professionals seeking enhanced system protection.

Conclusion

Water system commissioning remains one of the most important stages in protecting water quality and reducing microbiological risk.

Traditional chlorination continues to play a major role across the UK water industry, but chlorine dioxide is increasingly being recognised for its ability to address one of the most persistent challenges in building water systems: biofilm.

For organisations seeking effective disinfection, enhanced Legionella control and improved long-term water hygiene outcomes, chlorine dioxide deserves serious consideration as part of a modern water management strategy.

ChloroKlean provides a chlorine dioxide solution designed to support building water system disinfection, commissioning and ongoing water hygiene programmes across a wide range of commercial and residential applications.