Why New Buildings Can Still Develop Legionella Before Occupation

When people think about Legionella bacteria, they often associate it with ageing pipework, neglected water systems or poorly maintained buildings. In reality, even brand new buildings can develop Legionella if their water systems are not properly managed before occupation.

Recent reports surrounding the delayed opening of Worthing Integrated Care Centre, where Legionella was detected within the building’s water system, highlight an important lesson for developers, contractors, estates teams and facilities managers.

Although every situation is unique, it demonstrates that water hygiene should never be viewed as something that starts once occupants move into a building. Instead, effective Legionella control begins throughout construction, commissioning and handover.

Whether you’re preparing a healthcare facility, school, office, hotel or residential development, understanding the risks before occupation can help protect future occupants, reduce costly delays and support legal compliance.

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How Can a Brand New Building Develop Legionella?

A common misconception is that Legionella only affects older buildings. However, the bacteria simply require the right environmental conditions to multiply. The age of the building is far less important than how its water system has been managed.

During construction, pipework may be installed months before a building is occupied. If water remains stagnant within the system due to construction delays, phased commissioning or reduced water usage, conditions can become favourable for bacterial growth.

Several factors can increase the risk, including:

• Extended construction programmes
• Delayed occupation
• Low water turnover
• Infrequently used outlets
• Dead legs within pipework
• Poor commissioning practices
• Inadequate temperature control
• Biofilm development

Understanding these risks is the first step in effective water hygiene management. If you’d like to learn more about the wider causes of Legionella, read our related guide, Legionella Control: Don’t Ignore It.

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Construction Delays Can Increase Legionella Risks

Large construction projects rarely progress exactly to schedule. Delays caused by supply chain issues, phased fit-outs, planning changes or contractor availability may leave completed water systems unused for weeks or even months.

When water remains static for prolonged periods:

• Disinfectant levels can reduce.
• Water temperatures may enter ranges that encourage bacterial growth.
• Biofilm can begin developing inside pipework.
• Sediment may accumulate within tanks and outlets.
• Water quality may deteriorate before occupants even enter the building.

The recent reports regarding Worthing Integrated Care Centre serve as a reminder that even newly completed buildings should have robust water hygiene procedures in place before opening.

Rather than assuming a new installation is automatically safe, duty holders should ensure appropriate commissioning, flushing and monitoring have been completed before the building becomes operational.

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Why Healthcare Buildings Require Extra Attention

Healthcare environments deserve particular attention because many occupants may be more vulnerable to infections, including Legionnaires’ disease.

Hospitals, integrated care centres, GP surgeries and care homes often have:

• Extensive hot and cold water systems
• Numerous showers and outlets
• Clinical equipment connected to water supplies
• Complex pipework layouts
• Vulnerable patients with weakened immune systems

This is why healthcare estates teams typically adopt comprehensive water hygiene management programmes throughout the building’s lifecycle, beginning well before patients arrive.

If you manage healthcare premises, you may also find our article Legionella: A Special Approach for the Care Sector useful.

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What Should Happen Before a Building Is Occupied?

Preparing a building for occupation involves far more than completing construction works. Water systems should also be assessed to confirm they are safe for normal use.

Typical pre-occupation activities include:

Water Hygiene Activity	Why It Matters
Legionella Risk Assessment	Identifies potential hazards within the water system
System flushing	Removes stagnant water from pipework
Temperature monitoring	Confirms hot and cold water remain within recommended control ranges
Water sampling where appropriate	Provides additional verification of system condition
Tank inspections	Checks cleanliness and integrity
Commissioning records	Demonstrates compliance and provides an audit trail

These activities help provide confidence that the water system is operating as intended before occupants begin using the building.

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Who Is Responsible for Water Hygiene Before Occupation?

Responsibility for managing Legionella risks may change throughout the lifecycle of a construction project.

Depending on the project stage, responsibility could involve:

• Developers
• Principal contractors
• Building owners
• NHS Trusts
• Estates managers
• Facilities management providers
• Duty holders responsible for the premises

Once a building becomes occupied, the responsibility for ongoing Legionella management generally transfers to the organisation responsible for maintaining the water system.

Compliance should always be supported by suitable documentation, regular reviews and clearly defined responsibilities.

For further information on legal responsibilities, read our article Legionella Compliance Isn’t Voluntary.

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Buildings Most at Risk Before Opening

While every building should have an appropriate water hygiene strategy, certain property types can present greater risks due to their size, complexity or occupancy profile.

Building Type	Why Additional Care Is Needed
Hospitals	Complex water systems and vulnerable patients
Care homes	Residents may be more susceptible to infection
Hotels	Delayed openings or seasonal occupancy
Schools	Long holiday closures and periods of reduced use
Universities	Large estates with varying occupancy levels
Offices	Phased occupation following construction
Residential developments	Empty properties awaiting completion or sale

Different buildings require different control measures, which should always be based on a suitable Legionella Risk Assessment.

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Why Water Sampling Can Support Building Handover

Water sampling is often misunderstood.

Sampling is not intended to replace good water hygiene management or routine monitoring. Instead, it may be used as one part of an overall strategy to help verify that control measures are working effectively or to investigate specific concerns.

Depending on the building and its risk profile, sampling may support:

• Commissioning programmes
• Validation of control measures
• Investigation following prolonged stagnation
• Ongoing compliance monitoring
• Healthcare water safety plans

Learn more in our guide What Is Legionella Water Sampling Actually Used For?

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Water Hygiene Doesn’t End Once Occupants Move In

Occupation marks the beginning of ongoing water hygiene management, not the end.

Once a building is operational, duty holders should implement a structured programme that may include:

• Regular temperature monitoring
• Planned outlet flushing
• Tank inspections and cleaning
• TMV inspection and servicing
• Legionella Risk Assessment reviews
• Water sampling where appropriate
• Accurate compliance records

As buildings evolve, occupancy changes, refurbishment works or alterations to the water system may require existing control measures to be reviewed.

You may also find these related articles helpful:

• Is Your Water Legionella Free?
• Avoiding Troubled Waters: Legionella Control
• Legionella Risks in Your Workplace
• Fire and Water Safety in Schools

Together, these resources explain how effective water hygiene management supports safer buildings across a range of sectors.

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How Swiftclean Can Help

Managing water hygiene throughout construction, occupation and ongoing building management requires specialist knowledge and practical experience.

Swiftclean supports organisations across healthcare, education, commercial property, manufacturing, hospitality and the public sector with a comprehensive range of water hygiene services.

Whether you’re preparing a newly completed development for handover or reviewing an existing building’s water management programme, our experienced specialists can help ensure your systems remain compliant and effectively managed.

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Preparing a Building for Occupation?

Don’t wait until occupants move in to think about water hygiene.

Swiftclean’s specialists can help you assess, commission and manage water systems throughout construction, handover and ongoing occupation.

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Frequently Asked Questions About Legionella in New Buildings

Can a new building develop Legionella?

Yes. New buildings can develop Legionella if water remains stagnant during construction, delayed occupation or phased commissioning. Effective water hygiene management should begin before the building is occupied.

Why does stagnant water increase Legionella risk?

Stagnant water can allow disinfectant levels to decline while temperatures become more favourable for bacterial growth. Biofilm may also develop within pipework, creating an environment where Legionella can multiply.

Should new buildings be flushed before opening?

Yes. Flushing forms an important part of the commissioning process and helps remove stagnant water from the system before normal occupation begins.

Is water sampling always required?

Not necessarily. Water sampling may be appropriate depending on the building, its risk profile and the findings of the Legionella Risk Assessment. It should form part of a wider water hygiene management strategy rather than being relied upon in isolation.

Who is responsible for Legionella before a building opens?

Responsibility varies depending on the project stage and may involve developers, contractors, building owners or duty holders. Once the building becomes operational, responsibility typically transfers to the organisation managing the premises and its water systems. Read more in our blog: Who Is the Responsible Person? 

Can construction delays affect water quality?

Yes. Extended construction periods or delayed occupation can increase water stagnation, making it important to review water hygiene procedures before handover and occupation.

Why is Legionella a particular concern in healthcare buildings?

Healthcare facilities often contain extensive water systems and may accommodate patients who are more susceptible to infection. This makes effective water hygiene management particularly important from both a safety and compliance perspective.