Water Tank Disinfection: Chlorine vs Chlorine Dioxide

Introduction

Water storage tanks play a critical role in maintaining a safe and reliable water supply throughout commercial, industrial and residential buildings.

Whether serving a hotel, care home, hospital, holiday park, school or office complex, water storage tanks must be maintained in a condition that supports water quality and minimises microbiological risk.

Over time, tanks can accumulate:

• Sediment
• Scale
• Organic contamination
• Corrosion products
• Biofilm
• Microbial growth

As a result, periodic cleaning and disinfection are essential components of any water hygiene programme.

For decades, chlorination has been the traditional method used to disinfect water tanks and associated pipework. However, increasing attention is being given to chlorine dioxide due to its effectiveness against biofilm and its established role within water hygiene and Legionella control programmes.

This article compares chlorine and chlorine dioxide for water tank disinfection and explores how each approach can contribute to maintaining safe water systems.

Why Water Tank Disinfection Matters

Water storage tanks are often located out of sight and out of mind.

Despite this, they remain one of the most important components of a building's water infrastructure.

Poorly maintained tanks can contribute to:

• Legionella growth
• Pseudomonas contamination
• Increased bacterial counts
• Water quality failures
• Regulatory non-compliance
• Customer complaints

Routine inspection, cleaning and disinfection help ensure that water entering the distribution system remains of an acceptable quality.

Common Sources of Water Tank Contamination

Even well-designed systems can become contaminated over time.

Typical contamination sources include:

Dust and Debris

Poorly sealed tanks may allow external contamination to enter.

Sediment

Mineral deposits can accumulate on tank floors.

Corrosion Products

Older systems may release corrosion particles into the tank.

Organic Material

Leaves, insects and airborne contamination can introduce nutrients.

Biofilm

Microorganisms attach to internal surfaces and develop protective biofilm layers.

Stagnation

Low water turnover encourages microbial growth.

Understanding the Role of Biofilm

Biofilm is one of the most important factors affecting water tank hygiene.

Once microorganisms attach to internal surfaces, they can begin forming a protective matrix that supports bacterial survival.

Biofilm may develop on:

• Tank walls
• Tank floors
• Inlet pipework
• Outlet pipework
• Ball valves
• Internal fittings

Within this environment, microorganisms become significantly more difficult to remove.

This is why effective water tank disinfection requires more than simply killing free-floating bacteria.

The objective is to address the biofilm structures that support ongoing contamination.

Traditional Chlorination

Chlorination remains the most widely used method of water tank disinfection.

Typical chlorination programmes involve:

1. Cleaning the tank.
2. Refilling with water.
3. Dosing chlorine.
4. Maintaining contact time.
5. Flushing the system.
6. Verification sampling.

Advantages include:

• Established procedures
• Familiarity among contractors
• Widely available products
• Straightforward testing methods

However, chlorination can face challenges when significant biofilm is present.

What Is Chlorine Dioxide?

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

It differs significantly from chlorine in both chemistry and behaviour.

Key characteristics include:

• Strong microbiological performance
• Excellent biofilm penetration
• Reduced pH sensitivity
• Lower formation of chlorinated organic by-products
• Established use in Legionella control programmes

These characteristics have contributed to increasing interest in chlorine dioxide for water tank disinfection.

Chlorine Dioxide and Water Tank Hygiene

The primary goal of tank disinfection is not simply to kill microorganisms present at the time of treatment.

The goal is to reduce the conditions that support future microbial growth.

Because biofilm plays such an important role in contamination, technologies capable of penetrating biofilm often receive significant attention.

Potential benefits of chlorine dioxide include:

• Improved biofilm penetration
• Enhanced microbial control
• Reduced bacterial sheltering
• Improved access to contaminated surfaces
• Support for long-term water hygiene objectives

Chlorine vs Chlorine Dioxide

Biofilm Penetration

Chlorine

Good surface disinfection performance but can be limited by biofilm thickness and organic loading.

Chlorine Dioxide

Demonstrates excellent penetration of biofilm structures and is frequently selected where biofilm management is a priority.

Legionella Control

Chlorine

Widely used and effective when correctly applied.

Chlorine Dioxide

Frequently utilised in Legionella control programmes due to strong microbiological activity and biofilm penetration capabilities.

Pseudomonas Control

Chlorine

Effective against free-floating bacteria.

Chlorine Dioxide

Often selected where persistent bacterial contamination and biofilm are concerns.

pH Sensitivity

Chlorine

Performance decreases as pH rises.

Chlorine Dioxide

Maintains effectiveness across a broad pH range.

Odour

Chlorine

Often associated with noticeable chlorine smells.

Chlorine Dioxide

Typically produces less noticeable odour.

Corrosion Potential

Chlorine

Can contribute to corrosion under certain conditions.

Chlorine Dioxide

Often considered less aggressive towards system materials when correctly applied.

Water Tank Disinfection Process

A typical water tank disinfection programme includes:

Step 1: Inspection

The tank should be inspected for:

• Damage
• Sediment
• Biofilm
• Corrosion
• Contamination

Step 2: Cleaning

Physical cleaning removes:

• Debris
• Sediment
• Scale
• Loose contamination

Step 3: Disinfection

A suitable disinfectant is introduced.

The objective is to ensure contact with all internal surfaces.

Step 4: Contact Time

The disinfectant must remain in contact with surfaces for the required period.

Step 5: Flushing

The system is flushed to remove residual disinfectant.

Step 6: Verification

Water quality testing confirms successful completion.

Typical Applications

Water tank disinfection may be required following:

• New installations
• Refurbishment works
• Repairs
• Contamination incidents
• Legionella detections
• Periodic maintenance programmes

Sectors That Benefit From Effective Tank Disinfection

Hotels

Large water demand and complex systems increase water hygiene challenges.

Holiday Parks

Seasonal occupancy can lead to stagnation.

Care Homes

Vulnerable occupants require effective water quality management.

Hospitals

Enhanced water hygiene controls are often necessary.

Schools and Universities

Extended holiday periods may increase water age.

Commercial Buildings

Variable occupancy can affect system performance.

Example ChloroKlean Dosing Guide

The following example demonstrates approximate chlorine dioxide concentrations.

Assuming:

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

Actual dosing should always be based on site-specific requirements, system conditions and appropriate verification testing.

Why Water Hygiene Contractors Are Evaluating Chlorine Dioxide

The increasing focus on biofilm management has encouraged many water hygiene professionals to review alternative disinfection technologies.

Factors driving interest include:

• Legionella control
• Biofilm management
• Long-term system performance
• Reduced pH dependency
• Improved microbiological outcomes

As understanding of biofilm continues to evolve, many organisations are looking beyond traditional disinfection approaches.

Water Tank Disinfection and Long-Term Water Hygiene

Disinfection should not be viewed as a standalone activity.

Successful water hygiene management also requires:

• Risk assessments
• Temperature control
• Regular inspections
• Flushing programmes
• Monitoring
• Maintenance
• Biofilm management

The most effective programmes combine multiple control measures to reduce risk throughout the entire water system.

Choosing the Right Approach

There is no single solution suitable for every application.

The best disinfection strategy depends on:

• System design
• Water quality
• Occupancy patterns
• Microbiological risk
• Maintenance objectives
• Regulatory requirements

Traditional chlorination remains widely used and highly effective.

However, chlorine dioxide is increasingly being evaluated where enhanced biofilm control and long-term water hygiene performance are priorities.

Conclusion

Water storage tanks remain one of the most important components of any building water system.

Effective cleaning and disinfection help protect water quality, reduce microbiological risk and support compliance with water hygiene responsibilities.

While chlorination continues to be the traditional industry standard, chlorine dioxide is attracting increasing interest due to its ability to penetrate biofilm, support Legionella control and contribute to modern water hygiene programmes.

For organisations seeking a proactive approach to water system management, chlorine dioxide offers an effective tool that can complement broader strategies designed to maintain cleaner, safer water systems.

ChloroKlean provides a chlorine dioxide solution designed to support water tank disinfection, biofilm management and long-term water hygiene performance across a wide range of commercial and residential applications.