The following case study is from CHIRP Maritime’s Superyacht Feedback. It is the first superyacht-specific programme and publication dedicated to improving safety in the maritime industry through vital knowledge sharing, anonymous reporting, analysis and feedback via the Superyacht Maritime Advisory Board.

Initial report
“Upon taking over command of a superyacht, I set about conducting my usual due diligence. I noticed the water hadn’t been tested for a couple of years and sent off samples for lab analysis.”

CHIRP comment
This report highlights a significant potable-water-management issue identified during a change of command on a superyacht. Legionella levels were found to be significantly above acceptable limits and required testing had not been completed for an extended period. Without recent results, there was no objective evidence that the water system was safe, creating a potentially serious but hidden health risk.

The incoming captain identified the issue during routine checks before taking over the vessel. This early intervention provided an important safety barrier, and the prompt response from the water-treatment company helped ensure that appropriate control measures were introduced. Restricting water use, providing alternative arrangements and carrying out system cleaning reduced the immediate risk and protected those on board.

A particular concern was that several crew members indicated this was not an isolated event but something they had experienced previously. This highlights a wider industry challenge: repeated exposure to a problem can lead to it becoming accepted as normal rather than recognised as a condition requiring further investigation and improvement.

Legionella management requires a thorough understanding of how the bacteria develop and how exposure occurs. Separate drinking water tanks or filtration systems do not remove all risks. Legionella can multiply in water systems where conditions allow growth, and the greatest health risk occurs when contaminated
water is released as fine droplets from showers, taps or other outlets and then inhaled. Effective control relies on a comprehensive water safety programme, including appropriate system design, monitoring, temperature management, maintenance and disinfection procedures.

Passenger vessel operators have long recognised the seriousness of Legionella exposure. When cases occur, established protocols may include investigation, medical follow-up and contact tracing to understand potential exposure and protect affected persons. This demonstrates the importance of having clear procedures in place before an incident occurs.

The reports from MAB members suggesting recent similar cases indicate that Legionella remains an ongoing concern rather than a rare occurrence. This should reinforce the need for vigilance, not acceptance. Regular testing, accurate records, clear responsibility, and effective handover procedures are essential.

The key lesson is that a recurring problem does not become an acceptable condition. The master’s professional curiosity and early action demonstrate the value of challenging assumptions and verifying that safety-critical systems are operating as intended. Potable water systems must be managed with the same discipline applied to other critical systems on board.

Key issues relating to this report
Factors relating to this report
Complacency – Acceptance of an unverified water system condition due to previous experience without adverse consequences.

Norms (normalisation of deviation) – Contaminated water conditions and lack of testing had become viewed as an acceptable part of yacht operations.

Situational awareness – Insufficient recognition of Legionella as an airborne/aerosol exposure risk rather than only a drinking water issue.

Capability – Misunderstanding of the hazard mechanism and required controls; inadequate routine testing, monitoring and assurance of water-hygiene controls.

Key takeaways
Regulators: Oversight of preventive maintenance, hygiene assurance,and safety culture – “A hazardous biological condition existed undetected for years due to ineffective assurance of routine water-system testing and acceptance of degraded practice as normal.” From a regulatory perspective, the dominant deadly dozen factors are lack of awareness, norms (normalisation of deviation), and lack of procedures/standards, supported by weak safety management oversight.

Managers: Vessel safety governance, maintenance control, and risk escalation – “Critical water system controls had lapsed into routine neglect, with no effective escalation or verification of biological contamination risk until independent testing was initiated.” The outgoing command’s reassurance that the condition was “normal” demonstrates entrenched normalisation of deviation. There is also a clear gap between operational knowledge (the health risks of aerosolised Legionella) and on-board practice, indicating a weak transfer of safety-critical knowledge. Managerial focus should be on ensuring that water safety systems are actively managed, not assumed safe due to historical routine.

Seafarers: Operational awareness, challenge culture and hazard recognition – “At the crew level, the dominant deadly dozen factors are lack of awareness, complacency and lack of knowledge”. The belief that the condition was “normal” reflects the normalisation of deviance, in which prolonged exposure to degraded standards becomes accepted practice.

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