Understanding Biofilm Development and Compliance Risks

Date: 10/10/2025 
Read Time: 9 minutes
Author: Dr. Surani McCaw, B.E. (Chemical) 

Key points:

• Facility managers must actively monitor internal water systems, as town water alone may not be safe. 

• Take responsibility beyond the property meter to prevent microbial growth in plumbing. 

• Use continuous monitoring alongside grab sampling to detect hidden biofilms and prevent endotoxin risks. 

• Schedule quarterly preventive maintenance: avoid excessive servicing that could increase contamination 

Safe and reliable water systems are essential in healthcare and high-purity applications, yet they are often misunderstood as "set and forget." Even when town mains water meets the Australian Drinking Water Guidelines (ADWG), internal plumbing systems can harbour microbial growth, particularly biofilms, that present risks to patient safety and regulatory compliance. Routine monitoring, including grab sampling, provides only a snapshot of water quality and may not capture conditions conducive to biofilm development or endotoxin accumulation. Effective water system management therefore requires a combination of continuous monitoring, preventive maintenance, and well-designed operational controls to minimise microbial risk and ensure long-term system performance. 

In Australia, water supplied from the town mains generally complies with the Australian Drinking Water Guidelines (ADWG). However, a facility should never assume that this supply is automatically fit for its intended purpose. 

The responsibility of the water authority ends at the property's water meter. Beyond this point, the authority has no control over factors that may influence water quality within the facility's internal plumbing network. Consequently, it is the responsibility of the property owner or facility manager to identify, assess, and manage any risks to water quality within their infrastructure. 

Although water utilities are required to supply safe drinking water up to the property boundary, the ADWG does not prescribe a minimum residual chlorine concentration that must be maintained throughout the distribution network. Consequently, some facilities may not receive a consistent or adequate residual disinfectant level, increasing susceptibility to microbial regrowth, particularly in areas prone to stagnation, dead legs, or elevated water temperatures. 

In Australia, regulation of drinking water quality is managed at the state and territory level, with each jurisdiction adopting the ADWG as the national reference framework. 

Each water treatment system must be designed based on historical and current water quality data provided by the relevant water authority. Its long-term performance depends on the robustness of the treatment processes, the quality of equipment employed, and the ongoing preventative maintenance of the system. Regardless of design integrity, a water treatment system is never "set and forget." It requires continuous monitoring, maintenance, and validation to ensure ongoing compliance and safety. 

Compliance to a standard or guideline is generally assessed by collecting a single, discrete water sample at a specific point in time, typically monthly, and location within a system, representing the instantaneous conditions at that moment. This sampling process is known as "grab sampling". Unlike composite or continuous sampling, a grab sample does not account for temporal variations in water quality that may occur between sampling events. 

Facilities should never assume that a water treatment plant is operating optimally simply because routine grab samples indicate microbial counts within guideline limits. Grab sampling provides only a snapshot in time and may not capture conditions that promote microbial growth between sampling events. 

To accurately assess the health of a water treatment plant, it is essential to understand the stages of biofilm development and how they influence microbial activity within the system. Interpreting grab sample results in the context of biofilm behaviour provides a more realistic indication of system hygiene and the effectiveness of control measures. 

Microorganisms in natural environments, whether in water or air, exist either in a planktonic (free-living) state or as part of an attached community known as a "biofilm". Biofilm formation is typically preceded by the development of a conditioning film (CF), a surface layer formed by the adsorption of organic and inorganic molecules from the surrounding environment. This conditioning film modifies the physicochemical properties of the surface, creating a more favourable environment for microbial attachment. 

In water distribution systems, the internal surfaces of pipework become coated with a conditioning film within seconds of contact with water. The composition of this film varies depending on source water characteristics and treatment processes. The subsequent attachment of microorganisms to this surface occurs in two stages: reversible adhesion, followed by irreversible adhesion as cells anchor more firmly, begin to produce extracellular polymeric substances (EPS), and form microcolonies. 

The figure below (adapted from Kerr et al., 2003) illustrates the key stages of biofilm development. 

In a well-designed and hydraulically balanced water system, conditions favour reversible adhesion, and the potential for secondary colonisation and biofilm maturation is significantly reduced through the maintenance of appropriate water velocities and flow regimes.

However, if conditions become conducive to biofilm establishment, such as prolonged stagnation, nutrient accumulation, or suboptimal temperature control, irreversible adhesion can occur, leading to the development of mature biofilms. Once mature biofilms are established, bacterial control becomes extremely difficult, often resulting in persistent microbial contamination and long-term regulatory non-compliance.

With reversible adhesion, continuous and consistent compliance can be achieved through routine automatic thermal disinfection. The appropriate disinfection frequency, however, must be determined through both routine sampling and preventive maintenance.

• Under conditions that inhibit microbial growth (e.g. systems operating continuously at ≥65°C), weekly thermal disinfection is typically sufficient to maintain reversible adhesion.
• Under conditions conducive to microbial growth (e.g. nutrient-dense water at 25–45°C), daily thermal disinfection may be necessary to prevent irreversible biofilm establishment and maintain compliance.

Ultimately, the effectiveness of disinfection is strongly influenced by system design integrity, operational consistency, and maintenance frequency.

Inconsistent grab sample results, where compliance is sometimes achieved and sometimes not, are often influenced by the intermittent detachment of primary colonisers from developing biofilms. In neglected systems, persistently high bacterial counts exceeding compliance limits are typically caused by co-adhesion, microbial migration, and the sloughing of mature biofilm communities, which can contaminate the entire piping network and associated downstream equipment.

Systems in this state are generally considered beyond recovery, as disinfection cycles may trigger the release of high concentrations of endotoxins. At elevated concentrations, and depending on water chemistry, endotoxins can aggregate and adsorb to internal surfaces. Under these conditions, even validated endotoxin-retentive filters may be unable to reduce endotoxin to concentrations considered safe for patients and staff.

Preventive system design and maintenance are the most effective long-term strategies for managing microbial risk. Prevention is achieved through correct engineering of water systems and the implementation of structured preventive maintenance programs.

An appropriate balance in maintenance frequency is critical, as excessive site attendance and repeated handling of system components can increase the risk of cross-contamination and microbial introduction into the water.

In most healthcare and high-purity water applications, quarterly (three-monthly) preventive maintenance is considered optimal. More frequent visits, such as monthly servicing, can increase the likelihood of recontamination while offering limited operational benefit and reduced cost-effectiveness.