Biofilm in Water Systems: The Hidden Threat Inside Building Pipework

Introduction

When most people think about water hygiene risks, they think about bacteria floating freely within water.

In reality, one of the greatest threats to water quality often cannot be seen at all.

It exists attached to the inside surfaces of pipework, storage tanks, valves, fittings and outlets.

This threat is known as biofilm.

Biofilm is one of the most important factors influencing Legionella control, Pseudomonas management, water system hygiene and long-term disinfection effectiveness. Despite its importance, biofilm remains poorly understood by many building owners and facilities managers.

Understanding biofilm is essential for anyone responsible for managing:

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

This article explains what biofilm is, why it develops, how it affects water quality and why chlorine dioxide has become an increasingly important tool in biofilm management programmes.

What Is Biofilm?

Biofilm is a structured community of microorganisms attached to a surface and surrounded by a protective matrix.

The microorganisms produce a slimy layer known as extracellular polymeric substance (EPS).

This protective coating allows bacteria to:

• Attach to surfaces
• Share nutrients
• Communicate with each other
• Resist environmental stress
• Survive disinfectant exposure

Within water systems, biofilm can develop on:

• Pipework
• Water storage tanks
• Valves
• Shower hoses
• Tap outlets
• Heat exchangers
• Flexible connectors
• Dead legs

Once established, biofilm becomes significantly more difficult to remove than free-floating microorganisms.

Why Biofilm Forms

Biofilm development is a natural process.

Virtually every water system will experience some degree of biofilm formation.

Factors that encourage biofilm growth include:

Water Stagnation

Low flow rates and stagnant water provide ideal conditions for microorganisms to attach and multiply.

Temperature

Warmer temperatures accelerate microbial activity.

Nutrients

Organic matter provides food for microbial growth.

Pipe Surface Condition

Rough or damaged surfaces create areas where microorganisms can establish colonies.

Scale Deposits

Mineral scale provides additional surfaces for microbial attachment.

Corrosion Products

Corrosion can create protective environments that encourage bacterial growth.

How Biofilm Develops

Biofilm formation occurs in several stages.

Stage 1: Initial Attachment

Individual microorganisms attach to pipe surfaces.

Stage 2: Colonisation

Additional bacteria join the developing colony.

Stage 3: Matrix Formation

The microorganisms begin producing a protective matrix.

Stage 4: Maturation

The biofilm thickens and becomes increasingly complex.

Stage 5: Dispersal

Portions of the biofilm detach and release microorganisms into the water.

This continuous cycle allows contamination to persist even when water samples appear satisfactory.

Why Biofilm Is a Problem

Biofilm creates multiple challenges for water hygiene management.

Protection Against Disinfectants

Biofilm acts as a physical barrier.

Disinfectants may struggle to penetrate deeply enough to reach microorganisms embedded within the structure.

Microbial Reservoir

Biofilm can act as a long-term reservoir for bacteria.

Even when free-floating microorganisms are reduced, the biofilm may remain intact.

Recolonisation

Bacteria released from biofilm can recolonise other areas of the system.

Reduced Water Quality

Biofilm can contribute to:

• Taste issues
• Odour problems
• Discolouration
• Increased bacterial counts

Increased Maintenance Costs

Persistent biofilm can increase the frequency of:

• Sampling
• Flushing
• Disinfection
• Remedial works

Biofilm and Legionella

One of the biggest concerns associated with biofilm is its relationship with Legionella.

Legionella bacteria often survive within biofilm environments.

Biofilm provides:

• Protection
• Nutrients
• Stable conditions

This can allow Legionella populations to persist despite routine disinfection.

For this reason, effective Legionella management increasingly focuses on biofilm control rather than simply maintaining disinfectant residuals.

Biofilm and Pseudomonas

Pseudomonas aeruginosa is another microorganism strongly associated with biofilm development.

Pseudomonas is particularly problematic because:

• It readily colonises surfaces.
• It can thrive within biofilm structures.
• It demonstrates significant resistance to environmental stress.

Healthcare environments often place particular emphasis on controlling biofilm due to the relationship between biofilm and Pseudomonas contamination.

Signs That Biofilm May Be Present

Biofilm is often invisible.

However, indicators may include:

• Recurring microbiological failures
• Persistent Legionella detections
• Repeated Pseudomonas detections
• Unexplained bacterial counts
• Slime deposits
• Discoloured outlets
• Odour issues
• Poor water quality trends

In many cases, biofilm may be present even when no obvious symptoms are visible.

Why Traditional Disinfection May Struggle

Traditional disinfectants can be highly effective against microorganisms suspended in water.

However, biofilm presents a different challenge.

When disinfectants contact biofilm:

• The outer layers react first.
• Penetration may be limited.
• Internal microorganisms may remain protected.

This can result in:

• Temporary reductions in bacterial counts.
• Survival of biofilm structures.
• Eventual recolonisation.

The challenge is not always killing bacteria.

The challenge is reaching them.

Chlorine Dioxide and Biofilm Management

Chlorine dioxide has attracted significant interest because of its ability to penetrate biofilm more effectively than many conventional disinfectants.

Unlike chlorine-based chemistries that can react rapidly with organic contamination, chlorine dioxide can diffuse into biofilm structures and oxidise key components.

Potential benefits include:

• Improved biofilm penetration
• Enhanced biofilm disruption
• Improved access to embedded microorganisms
• Reduced bacterial sheltering
• Improved long-term hygiene performance

These characteristics have contributed to its increasing use within water hygiene programmes.

Why HSG282 References Chlorine Dioxide

Within spa pool guidance, chlorine dioxide is specifically referenced as a biodispersant compound for removing:

• Biofilm
• Slime
• Fouling

This is significant because it recognises chlorine dioxide's ability to address one of the most persistent challenges in water systems.

The reference is not related to routine residual disinfection.

It specifically relates to biofilm control and remediation.

This distinction is important because biofilm management is often the foundation of effective long-term microbial control.

Chlorine Dioxide vs Traditional Chlorination for Biofilm

Where Biofilm Creates the Greatest Risk

Hotels

Variable occupancy creates periods of stagnation.

Holiday Parks

Seasonal operation increases water age.

Care Homes

Complex water systems require robust management.

Hospitals

Vulnerable occupants increase risk.

Schools

Periods of low usage occur during holidays.

Commercial Buildings

Changing occupancy patterns influence water demand.

Leisure Facilities

Large systems create multiple opportunities for biofilm development.

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 requirements should always be determined through site-specific risk assessment and testing.

Managing Biofilm Effectively

Successful biofilm management requires multiple control measures working together.

These may include:

• Risk assessments
• Good system design
• Removal of dead legs
• Temperature control
• Regular flushing
• Monitoring programmes
• Appropriate disinfection strategies
• Routine maintenance

Biofilm should not be viewed as a one-time problem.

It is an ongoing management challenge.

The Future of Water Hygiene

The water hygiene industry is increasingly recognising that microbiological control cannot rely solely on maintaining disinfectant residuals.

Understanding and managing biofilm is becoming central to:

• Legionella control
• Pseudomonas management
• Water quality improvement
• Long-term system performance

As awareness continues to grow, technologies capable of addressing biofilm effectively are becoming increasingly important within modern water hygiene programmes.

Conclusion

Biofilm is one of the most significant yet least visible threats within building water systems.

It provides protection for microorganisms, supports recolonisation and can undermine conventional disinfection programmes if left unmanaged.

For building owners, facilities managers and water hygiene professionals, understanding biofilm is essential for maintaining safe, compliant water systems.

Chlorine dioxide has gained increasing attention because of its ability to penetrate and disrupt biofilm structures, helping support modern water hygiene strategies and long-term microbial control programmes.

ChloroKlean provides a chlorine dioxide solution designed to support biofilm management, water system hygiene and effective control of microbial risks throughout commercial and residential water systems.