Water for building services isn’t entirely free from aquatic organisms; therefore, measures must be taken to guard against conditions that encourage the growth of water-borne pathogens such as Legionella.
To avoid potentially costly remedial works, the design of new buildings and their water systems should be controlled to ‘get it right the first time’, essentially to ‘design out’ risk, which in turn will lead to a safer water system having had the correct design, installation, commissioning, maintenance and operation.
Legionella risk in hot and cold water systems
During the design process, the responsibility for water safety, alongside all design health and safety matters under the Construction (Design and Management) Regulations (2015), belongs to the principal designer. They are required to correctly plan, manage, and coordinate the design works and any construction work that may be required.
All members of the design and construction team should focus their approach with the operational phase of the water systems at the forefront of their decisions. Accurate and rational design selections, based on risk assessment, help minimise Legionella risk and can reduce CapEx and OpEx. If phased demolitions are part of the project, the designers should consider the impact on the operational aspects of the parts of the water systems that remain operational but under changed characteristics.
All designers must understand their responsibilities concerning the control of potential water-borne pathogens, including Legionella, when designing hot and cold-water systems, whether they are for a new build, refurbishment works of an existing building or a water feature or process. They should ensure that collaborative working between client, Architect and mechanical designer exists and are part of the specific project water safety group.
Principal Designer Responsibilities
Projects and designs will differ hugely in size and complexity. Some may be a simple change of use of a room whereby a wash hand basin is being added, or at the other end of the scale we may have a new hospital wing or department. That said, equal care and consideration must be given to each project, regardless of complexity, to ensure that potential risk is not introduced from water-borne pathogens. If inherent risk is unavoidable, it must be As Low As Reasonably Practicable. (ALARP)
The Principal Designer is responsible for:
- In conjunction with the Client, developing a clear brief of the water system design, taking into account input received from those responsible for water safety including your Water Safety Group (WSG). The first aspect to consider is who the user is likely to be and what their level of susceptibility is to water-borne pathogens and scalding.
- Ensuring that the specification for the installation and the construction project (i.e., Project Specification) meets the requirements of the original design and requirements of the clients Water Safety Plan.
- Preparation of:
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- Design risk assessment with a particular focus on Legionella control and scalding risk.
- Dedicated water systems drawings including schematic drawings that, as a minimum, meet the requirements of BS8580 – Water quality – Risk assessments for Legionella control. Code of Practice.
- Project specification and project / Legionella sampling plan for approval by the WSG.
- Commissioning brief for approval by the WSG.
- Information required to support the written scheme of control during the construction and operational phases.
- Design risk assessment with a particular focus on Legionella control and scalding risk.
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Architects
Typically, the Architects' contribution to the design of water systems relates to the selection of sanitaryware. Selections should be rational and focus on whether the hazard (water) can be removed or substituted. By removing water outlets/sanitaryware also removes the waste pipework which can be a key source of contamination.
In a healthcare facility, spatial awareness and separation distances between the outlets and bedspace are required to take account of the ‘splash zone’. It may be that splash screens are required, but all aspects such as these need to be in conjunction with the Trust.
Outlet selections should not be made in isolation of the mechanical designer. The need for thermostatic control should be on a risk-based approach, and the selection of outlets needs to factor in the pressure drop to ensure the combination of fixtures and fittings provides adequate flow and compliant backflow prevention.
Designers
Designers should consider how water systems will be operated, whether domestic water systems, water features or other systems that generate and disperse aerosols.
Designers should work with the Client to understand how water systems are operated and maintained. For example, rooftop photovoltaic installations often instigate the installation of multiple taps for cleaning purposes. These outlets are inherently used infrequently and require flushing. They are typically supplied by a storage tank providing fluid category 5 (FC5) backflow protection, often located where heat gain and poor maintenance access are concerns. Discussion with the water undertaker may establish whether FC3 rather than FC5 protection is appropriate. Alternatively, the outlets may be unnecessary if a cleaning contractor supplies deionised water to avoid mineral deposits on the glass.
Rational designs that avoid the unnecessary installation of plant and equipment and fixtures and fittings help to reduce the Legionella risk.
Regulation and Guidance
Some find this difficult to accept, but water hygiene and compliance should commence at RIBA Stage 0 – Strategic Definition and develop as the project progresses through the next phases through to handover.
The planning and design of water systems that are to be incorporated into a project, whether a new build, refurbishment, or extension of an existing system, can be a long and complex process. All engineering and building standards must be met at the initial design stage. Key documents that give some direction in this field are:
Other Considerations
All those involved in the design of water systems, for any sized project, should undertake Legionella training from a recognised service provider. If those involved in planning and design are aware of the risk from water-borne pathogens, it becomes easier to avoid those risks in the first instance, avoid them in the future, and at least put mitigation in place to manage residual risks to acceptable levels.
Sustainability remains core to design and construction and benchmarks such as BREEAM, however, achieving BREEAM should not put users at an increased Legionella risk.
Learn more about our Water Safety: Management Training - Project Water Safety
Conclusion
Getting it “Right First Time” can be a lengthy and challenging process. It is much harder to rectify problems once the project is completed than it is to “design out” any issues at the design stage or rectify issues identified during the construction phase. Everyone involved in the design process must be aware of the potential risks associated with water-borne pathogens and understand their role and responsibilities within that design team. Communication is key… it’s good to talk!
Feel free to reach out if you have any questions about the issues mentioned above or if you would like to consult with one of our experts on water hygiene.
Editors Note: The information provided in this blog is correct at the date of original publication – October 2023. (Revised November 2026)
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