Legionella Control in Building Water Systems: Treatment Methods, UAE Standards and the Role of Estidama

Legionella control has become an important consideration for building owners, facility managers, consultants and water-treatment professionals in the UAE. Large buildings such as hotels, hospitals, residential towers, schools and commercial facilities can have complex hot- and cold-water distribution systems that, if poorly managed, may create conditions suitable for Legionella growth.

Legionella bacteria can multiply in warm, stagnant water and can become a health risk when contaminated water is dispersed as fine aerosols, such as through showers, cooling systems and certain water outlets.

Effective Legionella management is therefore not simply a matter of installing a disinfection system. It requires a combination of good system design, temperature management, circulation, cleaning, monitoring, flushing and, where required, water-treatment technologies.

What Is Legionella?

Legionella is a type of bacteria naturally found in water. Under favourable conditions, it can multiply in building water systems, particularly where water temperatures are suitable for bacterial growth, circulation is poor or sediment and biofilm have accumulated.

People can become infected primarily by inhaling contaminated water droplets or aerosols. This can result in Legionnaires’ disease, a potentially serious form of pneumonia.

Building water systems can present a higher risk when they contain:

• Hot-water storage tanks
• Long distribution pipework
• Low-flow areas and dead legs
• Infrequently used outlets
• Poorly maintained shower systems
• Accumulated sediment and biofilm
• Inadequate hot-water circulation
• Water temperatures favourable to bacterial growth

For this reason, Legionella control should begin at the design stage and continue throughout the operational life of the building.

Main Methods Used to Control Legionella

There is no single treatment method suitable for every building. The appropriate solution depends on the water system, building type, water quality, temperature regime, risk level and operational requirements.

1. Thermal Disinfection

Temperature control is one of the fundamental methods of Legionella management.

Legionella growth is strongly influenced by water temperature. Maintaining hot-water systems at appropriately high temperatures and ensuring adequate circulation can reduce the opportunity for bacterial growth.

Periodic thermal disinfection may also be used as a corrective measure where required.

However, temperature management must be carefully designed and controlled because excessively high water temperatures can create scalding risks. Therefore, temperature control should be combined with appropriate safety measures and monitoring.

2. Chlorination and Hyperchlorination

Chlorine is one of the most widely used disinfectants in water treatment.

Chlorination works by oxidising and damaging microorganisms. For Legionella control, chlorine can be applied as a continuous disinfectant residual or at higher concentrations for corrective disinfection, depending on the system and applicable requirements.

Hyperchlorination can be particularly useful during remediation following a confirmed or suspected contamination event.

However, chlorine effectiveness can be affected by water chemistry, organic matter, temperature, pH and the condition of the pipework. Chlorine levels therefore need to be monitored and controlled.

3. Chlorine Dioxide

Chlorine dioxide is increasingly considered for Legionella control in large building water systems.

One of its key advantages is its ability to maintain a disinfectant residual within the water distribution system. This makes it different from treatment technologies such as UV, which provide disinfection at the treatment point but do not normally leave a residual in downstream pipework.

Chlorine dioxide can penetrate biofilm more effectively than some conventional disinfectants and can be applied as part of a continuous water-treatment strategy.

It can be particularly suitable for:

• Hotels
• Hospitals
• Residential towers
• Healthcare facilities
• Large commercial buildings
• Facilities with extensive hot-water distribution networks

The system must be correctly designed, dosed and monitored to ensure safe operation and compliance with applicable drinking-water requirements.

4. Copper-Silver Ionisation

Copper-silver ionisation is another technology used for continuous Legionella control, particularly in building hot-water systems.

The system introduces controlled concentrations of copper and silver ions into the water. These ions can interfere with microbial cell structures and biological processes, helping to control Legionella and other microorganisms.

A major advantage is that copper and silver ions can provide ongoing protection within the distribution system.

Performance depends on factors such as:

• Water chemistry
• pH
• Temperature
• Flow conditions
• Pipework configuration
• Ion concentration
• System maintenance

Correct monitoring and control are therefore essential.

5. Ultraviolet (UV) Disinfection

UV disinfection uses ultraviolet radiation to inactivate microorganisms by damaging their DNA.

UV can provide highly effective microbial reduction when the water receives the required UV dose and the equipment is properly maintained.

However, UV has an important limitation for Legionella control in building distribution systems: it does not provide a disinfectant residual.

This means that UV installed at the incoming water line or at a particular treatment point does not continue disinfecting water as it travels through the downstream pipework.

For this reason, UV is generally better considered as a supplementary treatment barrier rather than the sole Legionella-control measure for a large building distribution network.

6. Ozone

Ozone is a powerful oxidising agent capable of inactivating microorganisms.

It can be used in certain water-treatment applications, although its application for building-wide Legionella control requires careful system design because ozone does not provide a long-lasting residual throughout the distribution network.

Consequently, its suitability depends heavily on the specific application and treatment configuration.

Which Legionella Treatment Method Is Best?

There is no universal answer.

For example, a small building with a well-designed hot-water system may rely primarily on temperature management, circulation, flushing and monitoring.

A large hotel or hospital with extensive pipework may require a more comprehensive approach incorporating continuous secondary disinfection.

A practical comparison is:

The final technology selection should always be based on a Legionella risk assessment and the actual characteristics of the water system.

Legionella Requirements and Standards in the UAE

Legionella management in the UAE needs to be considered within the applicable local regulatory framework as well as recognised international guidance.

For Abu Dhabi, an important reference is the Abu Dhabi Occupational Safety and Health System Framework (OSHAD-SF), including CoP 12.0 – Prevention and Control of Legionnaires’ Disease.

The guidance focuses on preventing and controlling Legionnaires’ disease through proper management of water systems and risk.

Depending on the facility, stakeholders may also refer to internationally recognised standards and guidance, including:

• ASHRAE Standard 12 – Managing the Risk of Legionellosis Associated with Building Water Systems
• ASHRAE Standard 188 – Legionellosis: Risk Management for Building Water Systems
• HSE HSG274 – Legionnaires’ disease: Technical guidance

The exact requirements applicable to a project should always be verified against the latest requirements of the relevant UAE authority and the specific facility classification.

How Does Estidama Relate to Legionella Protection?

Estidama is Abu Dhabi’s sustainable development framework and is closely associated with sustainable building design, water efficiency, energy efficiency and environmental performance.

It is important, however, to distinguish Estidama requirements from Legionella-specific regulatory requirements.

Estidama should not be interpreted as a standalone Legionella treatment standard or as requiring a specific Legionella-control technology.

Instead, sustainable building design and responsible water-system management can contribute to reducing conditions that may increase Legionella risk.

For example, efficient water-system design, appropriate equipment selection, good operation and maintenance practices and effective water management can support the overall health and performance of a building water system.

Legionella-specific risk management should therefore be addressed through the applicable health and safety requirements, water-system risk assessment and recognised Legionella-control guidance, while Estidama requirements should be considered as part of the wider sustainable building framework.

Legionella Control Requires More Than Disinfection

One of the most important principles in Legionella management is that installing a disinfection system alone does not eliminate the risk.

A comprehensive Legionella management programme should consider:

• Water-system design
• Hot-water temperature control
• Adequate circulation
• Prevention of stagnation
• Removal of dead legs
• Regular flushing of low-use outlets
• Cleaning of storage tanks
• Control of sediment and biofilm
• Disinfection where required
• Regular water-quality monitoring
• Periodic Legionella testing where required
• Proper documentation and record keeping
• Corrective action when results exceed acceptable levels

This approach is often referred to as a Water Safety Plan or Legionella Water Safety Management Programme.

Conclusion

Legionella control is becoming increasingly important for UAE buildings with complex water distribution systems. Hotels, hospitals, residential towers, schools and other facilities need to consider Legionella risks as part of their water-system design, operation and maintenance.

Technologies such as thermal disinfection, chlorination, chlorine dioxide, copper-silver ionisation, UV and ozone each have different advantages and limitations.

The most effective strategy is not necessarily to select the strongest disinfectant, but to develop a treatment and management approach appropriate to the building’s risk profile and water system.

In many large facilities, continuous residual technologies such as chlorine dioxide or copper-silver ionization can provide an additional layer of protection throughout the distribution network, while thermal management, flushing, cleaning, monitoring and good system design remain fundamental components of Legionella control.

For UAE projects, the applicable local authority requirements should be reviewed together with recognized international standards and guidance. Estidama should be considered as part of the wider sustainable building framework, while Legionella-specific requirements should be addressed through the relevant health, safety and water-system management requirements.

A properly designed Legionella control program therefore combines technology with good engineering, regular monitoring and effective operational management.