New cruise ship rules call for more effective potable water and Legionella testing

Recent outbreaks of norovirus and Legionnaires’ disease aboard cruise ships over the past twelve months have reinforced the importance of effective water system management, with CM Technologies (CMT) urging cruise ship operators to align with new CDC sanitation rules and apply the same condition-monitoring discipline that is now standard in fuel management.

The U.S. Center for Disease Control and Prevention (CDC) updated its Vessel Sanitation Program standards in November 2025 marking a significant shift in cruise ship public health.For the first time, all cruise ships calling at U.S. ports are now required to monitor for Legionella.

“The revision represents a strengthening of environmental surveillance obligations,” said Uwe Krüger, joint Managing Director of CMT, a leading specialist in marine condition monitoring and onboard testing equipment.

“This is a major regulatory shift, moving the focus beyond acute gastroenteritis, caused by the norovirus, towards structured environmental pathogen control and auditable, data-driven performance verification. The revised standards significantly tighten expectations around potable water system integrity.”

All cruise ships calling at US ports with 13 passengers or more must now carry out documented risk assessments covering potable and recreational water systems, define monitoring frequencies, implement clear remediation protocols where issues are detected, and maintain verifiable records of corrective action.

The ruling coincides with a number of recent incidents that met CDC’s reporting threshold of 3% or more of a cruise ships’ complement reporting gastrointestinal symptoms during a voyage.

Over the course of the past 12 months a number of cruise ships were identified as having reported outbreaks of norovirus. And cases of Legionnaires’ disease were reported among passengers that had recently sailed on two cruise vessels.

“While gastrointestinal outbreaks are typically driven by person-to-person transmission, the Legionella cases underline the importance of maintaining strict temperature control, disinfectant management and circulation stability within potable and recreational water systems,” said Krüger.

CMT joint Managing Director David Fuhlbrügger furthered: “Pools, spa areas and whirlpools are breeding grounds but it is not enough to just measure chlorine levels and assume the water is clean. Operators must now demonstrate that disinfectant residuals are maintained within defined limits, not simply assume compliance. The filtration system and overall effectiveness of the management system must also be verified, requiring structured cleaning, monitoring and documentation.”

He furthered that showers are often overlooked, but they represent a specific risk. “Legionella transmission occurs through inhalation of aerosolised warm water. What we frequently see in practice is that operators sanitise the system after a positive test result but fail to remove scaling from shower heads. Limescale can harbour Legionella bacteria, allowing recolonization of the system. Effective control needs chemical sanitisation and physical maintenance.”

To support compliance with the enhanced monitoring requirements, CMT provides portable potable water testing kits capable of measuring chlorine residuals and dosing, along with indicators for the presence of coliform and enterococci and other bacteria. Dedicated Legionella testing kits are also available for structured surveillance programmes, enabling onboard verification rather than reliance on periodic laboratory analysis alone.

“In today’s regulatory environment, the ability to prove system performance is just as important as achieving it,” said Fuhlbrügger.

The CDC requirements will be enforced through port inspections, documentation review, sampling and outbreak investigations.