How Safe Is Your Ship’s Water?

Image of someone testing the water quality with the words, How Safe Is Your Ship's Water?

As Albert Szent-Györgyi, a Nobel Prize-winning biochemist, so eloquently observed, “Water is life’s matter and matrix, mother and medium. There is no life without water.” Water is undoubtedly essential to the very chemistry of life—it supports cellular functions in all living organisms from microbes to human beings—but it is also scarce and unevenly distributed. It may be the most abundant liquid on our planet’s surface, but only 3% of water on Earth is fresh water, the vast majority of which is difficult to access, either concealed deep underground or imprisoned in ice.

Every year on March 22 we celebrate World Water Day: an event highlighting the importance of fresh water and promoting the sustainable management of our resources. With the date imminent, now is an opportune moment to examine how operations in the maritime industry are ultimately dependent on fresh water and the public health controls required to ensure its safe provision.

Moreover, we will review studies on the quality of water on board ships and why the results advocate the need for all vessel owners, operators, and ship management companies to step-up and become “aquapreneurs”—a term coined by Indian businesswoman and philanthropist Roshni Nadar Malhotra—for water safety and the prevention of waterborne diseases.

What is Potable Water?

In the maritime industry, fresh water used on ships is known as potable water. Potable water simply means water that is safe to drink. More accurately, potable water is water that has been treated to remove harmful contaminants to meet drinking-water quality standards for human consumption. Potable water must be free from any microorganisms, parasites, chemicals, or other substances which, in the numbers or concentrations present, would not cause immediate or long-term illness.

Whether used for drinking, food production, recreational purposes, sanitation, or washing laundry, all vessels need an adequate supply of potable water. While some ships have the ability to convert seawater into fresh water through on board desalination processes, the majority of vessels fulfil their water needs by bunkering potable water from shoreside supplies when in port. Consumption is dependent on several variables including the type and size of vessel; however, to provide some context, a moderately-sized cruise ship may use upwards of 500,000 litres of potable water per day.

All potable water that a vessel bunkers or produces is stored in huge repositories known as potable water storage tanks. When needed, the water is distributed from these tanks around the ship using kilometers of piping to various hot and cold-water systems. With the exception of the bottled variant, water is one of the few resources on board not subject to the customary maritime hierarchies. Regardless of rank or status—from Master to Cadet, from a visiting company CEO to Ship Superintendent—the water they use is all the same.

The microbial contamination of potable water can endanger the health of crew and all who sail on board. Norovirus, Escherichia coli (E. coli), and Legionella bacterium are some of the primary sources of waterborne disease outbreaks associated with the complex water systems found on maritime vessels. These waterborne outbreaks are caused by a number of contributing factors including:

  • Contaminated water bunkered from ashore.
  • Inadequate control of cross-connections: a point in the plumbing system where the potable water supply is connected to a potential source of contamination.
  • Insufficient water treatment (i.e., disinfection).
  • Ingress of wastewater into the potable water system.

Given how critical the safe supply of potable water is to the operation of a ship, it ought to be reasonably expected that maritime companies would be leaders in the field of water safety. If so, the analysis published in studies that reviewed the microbiological and chemical quality of potable water on board ships is surprising.

The Presence of Indicator Organisms in Water

In October 2022, I attended an event in Athens, Greece organized by the EU SHIPSAN ASSOCIATION: The International Public Health Congress 2022 on Maritime Transport and Ports: Sailing to the Post-COVID-19 era’ . The event brought together scientists, government officials, maritime industry representatives, port administrators, and other associated organizations to discuss the latest evidence-based scientific data, best practices, and research in the field of maritime public health.

Two presentations predicated on the following articles were of particular interest and relevance to water safety: Potable Water Quality on Non-Passenger Ships Calling Belgian Ports and Legionella spp. Colonization on Non-Passenger Ships Calling at Belgian Ports. Both studies were based on the analysis of potable water samples collected at Belgian ports from non-passenger ships during Ship Sanitation Certificate (SSC) inspections conducted between 2010 and 2018.

Samples from 2,056 vessels were collected for microbiological analysis. Of these, 229 (11.1%) had at least one positive sample that indicated the presence of coliform bacteria, E. coli, or enterococci. An earlier study conducted between May and October 2005 on vessels—including cruise ships and ferries—docking in UK and Channel Islands ports discovered that from 335 ships, 54 (16.1%) also had one of these indicator organisms present.

Indicator organisms are microorganisms such as bacteria and viruses that are used as a proxy or “marker” to measure the overall hygienic quality in food, water, or the environment. Coliform bacteria, E. coli, and enterococci are some of the most common indicators in water sampling. Principle attributes that make a particular microorganism an ideal potable water indicator include:

  • Easily detected by inexpensive laboratory tests, even at low concentrations.
  • Normally absent in water not contaminated by feces.
  • As resistant to disinfection as the hardiest waterborne pathogen.

Coliforms encompass a large group of bacteria that can be found in our natural environment: on plants, in soil, and in the feces of humans and animals. Most types of coliform bacteria are harmless, but some can cause serious illness. Although their presence in water may not be directly related to fecal contamination, it does indicate that a contamination pathway exists. As the chlorine concentrations typically used in on board water treatment processes should be sufficient to neutralize them, their existence is likely the result of inadequate disinfection or post-treatment contamination.

In comparison, the presence of E. coli and enterococci in samples are direct indicators of fecal contamination and can cause a variety of symptoms if ingested. These symptoms include diarrhea, abdominal cramps, vomiting, urinary tract infections, and in rare cases, kidney failure. While the free chlorine residual measurements—the chlorine in the water that is available for disinfection to kill disease-causing pathogens—was not present in the Belgium study, the pH of the water was found outside optimum ranges in 20% of the ships.

The disinfectant power of chlorine is relative to the pH of the water. pH is a measure of how acidic or alkaline (basic) water is. As pH increases, chlorine becomes less effective. As it decreases, chlorine becomes more effective. However, if the pH is too low, the water turns corrosive, damaging piping and other water system components, which may lead to additional contamination problems.

Maintaining appropriate free chlorine concentrations is essential to protect the quality of potable water supplies on board ships, but it is not the only component of a water safety program. As the second Belgium study discovered, another potentially fatal bacterium was found lurking in the potable water distribution systems of the vessels analyzed.

Legionella in Potable Water Systems

From 2010 to 2018, 777 potable water samples were collected at Belgium ports from 401 different maritime vessels and analyzed for the presence of Legionella. Of those samples, 396 (51.0%) were positive for Legionella bacteria. The study states that over two-thirds of the ships tested had at least one positive Legionella sample.

Legionella bacteria are natural inhabitants of freshwater environments like lakes, rivers, and streams. They generally become a public health concern when they grow and propagate in man-made water systems, particularly in the large and complex types found in hotels, hospitals, office blocks, residential buildings, and ships. The most common form of Legionella transmission is the inhalation of contaminated aerosols—tiny droplets of water containing the bacteria—produced by systems such as air conditioning cooling towers, whirlpool spas (hot tubs), and showers.

There are over 60 known species of the bacteria, with the most common, Legionella pneumophila serogroup 1, accounting for 80-90% of Legionnaires’ disease cases. Legionnaires’ disease is a serious form of pneumonia (lung infection) with a case fatality rate of approximately 10%. Symptoms, which are very similar to other types of pneumonia, usually begin two to ten days after being exposed to the bacteria but can take longer.

Although not the only determinant, temperature is one of the most important environmental factors influencing the growth of Legionella in water systems. Legionella thrives at temperatures between 25°C and 45°C (77°F-113°F), with the optimum temperature for proliferation being 37°C (98.6°F). The bacteria are dormant below 20°C (68°F) and do not survive in temperatures maintained at 60°C (140°F) and above. Water stagnation, insufficient hygiene practices, and the presence of rust, scale, and organic matter that provide nutrients and protection for the bacterium, are some of the other main ingredients for Legionella propagation.

Since the late 1970s, there have been hundreds of documented cases of Legionnaires’ disease associated with ships: the majority of incidents taking place on passenger vessels such as cruise ships, river ships, and ferries. The disease is thought to be considerably underdiagnosed and underreported, making it difficult to estimate the true burden of the illness within the maritime industry.

Given the similarities with other forms of pneumonia and its long incubation period—the time between infection and the manifestation of symptoms—detecting travel-associated Legionnaires’ disease cases is challenging. In addition, there are many parts of the world where surveillance for such cases is not conducted. Notification and reporting varies country to country, and it’s a disease not always recognized by patients and healthcare providers alike. Its diagnosis requires specific laboratory tests such as a culture of lower respiratory secretions or a urinary antigen test.

For non-passenger vessels especially, where an on board doctor is not normally part of the crew complement, legionellosis cases—a term used for all infections caused by Legionella including both Legionnaires’ disease and a milder flu-like illness known as Pontiac fever—may go unnoticed.

The Age of Aquapreneurs

Maritime vessels are not obligated to disclose anomalies detected in routine water sampling to port health authorities: they are only required to report actual cases of infectious disease. Furthermore, many maritime companies do not conduct regular analysis of their potable water for the presence of Legionella or other opportunistic waterborne pathogens such as Pseudomonas aeruginosa. The absence of routine verification monitoring for microbes other than the common indicator organisms is likely a contributing factor in the high prevalence of Legionella contamination detected in ship water systems cited in similar studies.

The provision of safe potable water on board ships presents particular challenges for owners, operators, and ship management companies to navigate. Contamination can occur at any point in the water supply chain from the original water source to during bunkering, production, storage, or distribution. In future articles, we will discuss the range of water safety controls needed to provide the necessary assurance. However, given the breadth of studies available for review in regard to potable water quality on ships, the results indicate there is room for improvement.

The theme for World Water Day 2024 is “Leveraging Water for Peace”: how water can be a catalyst for universal harmony between communities and countries. While World Water Day is a time to reflect on the wider, global issues of fresh water, it’s also an opportunity for maritime companies to consider their role in water conservation. The remedial actions associated with water contamination events on ships generally involve the use of more water. With this realization comes a recognition that the prevention of such incidents can make a positive difference in water conservation efforts.

Every drop counts! MHS is ready to support your organization in enhancing water safety standards fleetwide through our portfolio of maritime public health services which include the development of Water Safety Plans, on board crew training, and quality assurance audits. To learn more about how MHS can help your company become an aquapreneur, book a consultation.