What Is Legionella and Why Does It Matter for Building Compliance?

Legionella is a group of bacteria that can grow in building water systems and cause Legionnaires' disease, a serious form of pneumonia, when contaminated water droplets are inhaled. For building owners and managers, it matters because water systems such as cooling towers, hot and cold water services, showers, and evaporative condensers can create the conditions for growth and spread. A Legionella risk assessment is therefore a standard part of building compliance, and it is often carried out alongside other surveying and inspection work.

What Legionella Is and How It Causes Illness

Legionella bacteria occur naturally in freshwater at low levels. Problems arise when they multiply in man-made water systems and are released as an aerosol — fine droplets or mist that can be breathed in. Key points:

• The disease: Legionnaires' disease is a severe respiratory infection. It is not spread person to person.
• The route of exposure: Inhalation of contaminated aerosols, not drinking the water.
• The conditions that favour growth: Water temperatures roughly between 20°C and 45°C, stagnant water, presence of nutrients such as rust, sludge, scale, and biofilm, and poor system design or maintenance.

High-Risk Water Systems and Conditions in Buildings

Not every water system carries the same risk. The following are commonly treated as higher risk:

Conditions that increase risk include dead legs and redundant pipework, infrequently used outlets, low water turnover, and systems where temperature control has failed.

Legal and Compliance Duties for Building Owners and Managers

In many jurisdictions, duty holders — typically the building owner, landlord, or facilities manager — are responsible for managing Legionella risk. The general pattern of these duties is to:

1. Identify and assess the risk from all water systems under their control.
2. Prevent or control the risk through design, temperature management, and maintenance.
3. Record the assessment, control measures, and monitoring results.
4. Review the assessment when systems change or at defined intervals.

The exact legal framework, thresholds, and record-keeping requirements vary by country and building type, so duty holders should confirm the specific regulations that apply to their property.

How Legionella Risk Assessment Fits into Surveying and Inspection

Legionella work overlaps with broader building compliance surveying. A risk assessment typically involves:

• Surveying the water systems — identifying all plant, pipework, outlets, and tanks.
• Recording conditions — temperatures, stagnation, condition of tanks and pipework, and any signs of contamination.
• Assessing and prioritising — rating each system's risk and recommending controls.
• Scheduling monitoring — temperature checks, cleaning, and sampling where required.

This is where mobile surveying software becomes relevant. Tools such as PocketSurvey are designed for structured, repeatable data collection in the field, and the same approach used for housing stock condition, asbestos, and fire safety surveys can be applied to Legionella inspections. The site describes its software as well-proven, fast, customisable, and easy to use, with a bespoke custom data collection system available — useful if you need to build a Legionella-specific inspection form. Note that pricing and access terms are not specified in the available information, so check directly with the provider.

Practical Prevention and Control Measures

Controls generally fall into a few categories:

• Temperature control: Store hot water hot enough and cold water cold enough to limit growth, and manage the points in between.
• Avoid stagnation: Remove dead legs, flush infrequently used outlets, and keep water moving.
• Keep systems clean: Control rust, scale, sludge, and biofilm, which provide nutrients.
• Use appropriate treatment: Where required, apply biocides or other water treatment.
• Maintain and monitor: Clean and disinfect systems, and record the results.
• Manage aerosols: Pay particular attention to cooling towers, showers, and spa pools.

What to Do Next

If you are responsible for a building, the practical starting point is to confirm who the duty holder is, identify every water system on site, and arrange a Legionella risk assessment. From there, build a monitoring schedule and keep records. If you collect this data in the field, a mobile surveying tool can help standardise the process — but the assessment itself should be carried out by someone competent to judge the risk.