A ship is not just a building that moves. It bunkers water, stores it in tanks, heats it through compact plant, sends it to cabins and showers, sometimes runs spas or pools, and may use air-conditioning or humidification systems that create their own wet surfaces. When water quality goes wrong, the same crew and passengers can be exposed repeatedly before the vessel reaches port.

That is why the small-boat answer is not enough for ferries, fishing vessels, commercial yachts and merchant ships. The ordinary HSE Legionella framework still matters, but UK maritime operators also need to read the Maritime and Coastguard Agency route: biological-agent duties for workers, ship fresh-water guidance, and specific ship air-conditioning advice.

MCA’s current MSN 1889 Amendment 5 gives detailed information for complying with the Merchant Shipping and Fishing Vessels (Health and Safety at Work) (Biological Agents) Regulations 2010 as amended. It says shipowners and employers must assess risks to those working on their ships from exposure to biological agents, and it explicitly includes work with air-conditioning and water-supply systems, swimming pools and spas among activities where exposure may arise [1].

The same notice applies broadly across UK registered vessels and government ships, and to commercially operated vessels including yachts, fishing vessels and vessels operating only on inland waters, with certain provisions also applying to non-UK ships in UK waters [1]. That matters because a commercial vessel cannot rely on a domestic “boat hygiene” checklist and stop there.

MCA’s fresh-water guidance, MGN 525, adds the provision-and-water layer. It explains that food hygiene principles and provision and maintenance of fresh water apply regardless of vessel age, size and type, and that prevention through risk assessment and management is one of the most effective ways to secure food and fresh-water safety [2]. It also points back to HSE’s ACoP L8 as practical advice for controlling Legionella where a work activity creates foreseeable exposure [2].

What makes ships different

The core Legionella mechanics are familiar: warm water, stagnation, biofilm and aerosol. The shipboard version is sharper because those conditions can stack.

Bunkered water. Water may be taken from different ports, stored, transferred and topped up. MSN 1889 notes that shipboard outbreaks have involved factors such as contaminated bunkered water, inadequate disinfection, potable water contaminated by sewage, and poor design or construction of storage tanks [1].

Compact, complex distribution. Cabins, crew accommodation, galleys, laundries, deck showers and technical spaces can sit close together, with heat sources and dead legs hard to access.

Intermittent use. Seasonal ferries, charter yachts, fishing vessels between trips, spare cabins and rarely used showers all create low-turnover outlets.

Aerosol assets. Showers, spa pools, hot tubs, decorative water features, pressure washers and pool features all create inhalation exposure. A vessel that carries passengers may also face travel-associated Legionnaires’ investigation if guests disperse after the voyage.

Air-conditioning systems. Ship air-conditioning can carry a separate Legionella concern. MCA’s MGN 38 identifies opportunities for contamination where water carryover, wetted cooler sections, spray-type humidifiers, condensate sumps or wet insulation are present, and recommends design, drainage, access, cleaning and maintenance countermeasures [3].

Field checklist for a vessel Legionella file

Use this as an evidence index, not a method statement. A competent person still has to set the control limits, inspection frequencies and sampling plan for the vessel.

Regulatory scope

  • Identify whether the vessel is a UK registered vessel, non-UK vessel in UK waters, fishing vessel, ferry, commercial yacht, passenger vessel or inland commercial vessel.
  • Record which MCA notices, HSE L8/HSG274 documents, port-health requirements and operator standards apply.
  • Name the shipowner/operator duty holder, master or delegated responsible person, and the competent water-safety adviser.

Water supply and storage

  • Map bunkering points, transfer lines, potable-water tanks, vents, overflows, pumps, calorifiers, return loops and distribution zones.
  • Keep records for water source, bunkering, tank inspection, cleaning, disinfection and any potable-water test results.
  • Check that tanks and distribution are protected from sewage cross-contamination, heat gain and stagnant sections.

Accommodation and outlets

  • List cabins, crew showers, passenger showers, galleys, laundries, medical spaces, deck showers and rarely used outlets.
  • Keep flushing, temperature and showerhead-cleaning records for low-use cabins and seasonal or spare accommodation.
  • Tie outlet checks to voyage pattern, refit periods, lay-up and return to service.

Pools, spas and passenger features

  • Treat spa pools and hot tubs as their own higher-risk systems under HSG282-style control, with chemistry, microbiological monitoring and cleaning records [4].
  • Include decorative fountains, spray features and pool balance tanks on the schematic if the vessel has them.

Air-conditioning and humidification

  • Inspect filters, cooler condensate sumps, drains, eliminators, humidifiers and wet insulation.
  • Record cleaning and maintenance of any water-spray humidification or wetted air-handling components.
  • Use MGN 38 as the ship-specific prompt for air-conditioning Legionella controls [3].

Incident readiness

  • Keep the risk assessment, schematic, sampling results, temperature records, disinfection certificates, air-conditioning maintenance records and responsible-person contacts in one retrievable file.
  • Know the port-health, MCA and public-health escalation route before a suspected case appears.

Where small-boat advice stops

The domestic-water logic in Legionella on boats, narrowboats and in marinas is still useful for a small freshwater tank and shower. It is not enough for a commercial vessel with workers, passengers, bunkered potable water, shipboard air-conditioning or spa systems. For those vessels, the record should show the MCA biological-agent and fresh-water route as well as ordinary HSE Legionella controls.

For passenger vessels, the travel link also matters. A guest can leave the ferry or cruise, develop symptoms days later, and be investigated through national or cross-border surveillance routes. Travel-associated Legionnaires’ disease and ELDSNet and travel-associated Legionnaires cover that investigation layer.

FAQ

Does ACoP L8 apply on ships?

MCA’s fresh-water guidance points to HSE’s ACoP L8 as practical Legionella control advice for undertakings involving a work activity, while MCA’s own merchant-shipping notices provide the maritime legal and operational context [2]. Treat L8/HSG274 as the control framework, then anchor the vessel file to the applicable MCA notices and the actual flag, route and operation.

Is ship air conditioning really a Legionella issue?

It can be. MGN 38 is specifically about contamination of ships’ air-conditioning systems by Legionella bacteria. The concerns are not ordinary dry air movement; they are wet components such as condensate sumps, water carryover, spray-type humidifiers and insulation that can become wet and harbour contamination [3].

Is a ferry or commercial yacht covered by the same advice as a narrowboat?

No. The basic biology is the same, but a commercial vessel with workers or passengers has a different evidence burden. MCA’s biological-agent notice covers commercially operated vessels, including yachts, fishing vessels and vessels operating on inland waters, so the file should not stop at a private-boat cleaning routine [1].

Next step

Pull the vessel’s water schematic and mark four things in different colours: bunkered-water path, stored potable-water tanks, aerosol outlets, and air-conditioning or humidification wet sections. If any colour cannot be traced to a named owner and a current record, that is the first gap to close.

Sources

  1. Maritime and Coastguard Agency, “MSN 1889 (M+F) Amendment 5: Biological agents regulations 2010”. https://www.gov.uk/government/publications/msn-1889-mf-amendment-5-biological-agents-regulations-2010/msn-1889-mf-amendment-5-the-merchant-shipping-and-fishing-vessels-health-and-safety-at-work-biological-agents-regulations-2010-as-amended
  2. Maritime and Coastguard Agency, “MGN 525 (M+F) Amendment 1: Guidelines for the provision of food and fresh water”. https://assets.publishing.service.gov.uk/media/5a80a22be5274a2e8ab5144d/MGN_525_Amd_1.pdf
  3. Maritime and Coastguard Agency, “MGN 38 (M+F): Contamination of ships air conditioning by legionella”. https://assets.publishing.service.gov.uk/media/5ece1cb7e90e0754dbf67b76/mgn038.pdf
  4. HSE, “Control of legionella and other infectious agents in spa-pool systems (HSG282)”. https://www.hse.gov.uk/pubns/books/hsg282.htm