Water safety plans


MTSea discusses Legionella and having a Water Safety Plan

Generally, it is accepted that consumption of contaminated water can cause illness. Less well appreciated is the risk to health from inhalation of water aerosol contaminated with Legionella. We commonly hear yacht crew say they do not need to manage on-board water because they do not drink it, but as this article explains there is nothing safe about this assumption.

Hotels and holiday apartments on land are required to test and treat their water to ensure Legionella is not a risk to health, it therefore makes sense that yachts accommodating guests and crew should take the same care, by introducing a robust Water Safety Plan.

What is Legionella and why is it dangerous? Legionella is a Gram-negative bacterium that can cause legionellosis, a pneumonia type illness called Legionnaires´ disease and a milder flu like illness called Pontiac fever. This bacterium can be found anywhere, in domestic, industrial and natural settings, it lives in soil and water. Legionella is only dangerous when it enters the lung in droplet or aerosol form.

Drinking water with legionella is not harmful as the bacteria is killed by acid in the stomach, nor is it contagious, though outbreaks are possible due to exposure to a common, contaminated source.

The likelihood of illness depends on the vulnerability of the individual, the concentration of Legionella in the water, the virulence of specific strains and the degree of exposure. Once infected the disease can be treated but if left untreated it can cause serious health problems and potentially death.

Exposure is possible is any situation where splashed or sprayed water can enter a person´s airway in small enough form to reach the lungs. This is why it is so important to check the water quality everywhere on a yacht not just in the drinking water in the galley or the bar.

MTSea What are the environmental conditions that favour the growth of legionella?
Management of all potable water is about controlling the levels of micro-organisms that live in the water supply, it is not about their total eradication. Legionella can get on board in small numbers in municipally supplied water.

Authorities constantly monitor and treat their water to ensure their supply is safe, but the disinfectants they add to the water degrades and cannot be relied upon to give continuing protection. Storage tanks are not sterile and even when water is made on board it needs to be monitored, disinfected and tested regularly. Ensuring water is safe for use is a continuous process.

Legionella can live happily in any body of freshwater especially where the current is slow or absent. Even in systems where water is treated if the water does not move, as in dead legs or return pipework Legionella can take hold and thrive.

Water systems on a yacht are a perfect breeding ground, the environment is warm, some pipework may remain unused for extended periods of time and left to its own devices, damp warm pipework will develop its own layer of slime providing organisms a place to hide from disinfectant chemicals, this layer is called biofilm.

Temperature wise Legionella can survive cold, and heat up to 70ºC, its happiest temperature where it reproduces rapidly at is between 35ºC and 37ºC. In summer it is not unusual for the cold tap to run warm to the touch so in this zone MTSea see a higher than expected rate of infections on yachts it tests. Last year the infection rate was 11%, our laboratory advises 4.7% is normal.

What exactly is biofilm?
Biofilm is a bacterial, self-produced protective slime made up of an extracellular polymeric substance (EPS), bacterial cells, amoebae (often a host of Legionella), other proteins, organic materials, and water.

Once formed, it can provide a protective environment where bacteria can hide from anti microbial agents. (Endosan website 2024).



How to prevent Legionella

  • Have a Water Safety Plan and SOP
  • Provide crew training appropriate to their role on board.
  • Protect water from contamination during bunkering and avoid pipework connections with other systems.
  • Continuously treat potable water to attain a safe, residual level of disinfection in the water. This is not possible with sporadic treatment.
  • Have a regular testing routine that includes on board testing and regular 3rd party laboratory checks.
  • Complete routine periodical system disinfection and shock treatment when indicated by the testing results.
  • Keep accurate records and review the process on a regular basis.

Water Disinfectants why change from chlorine?
Chlorine is a cheap effective disinfectant. At recommended dose levels it is considered safe for human consumption. So why change, what are the issues?

  • Chlorine is not effective at penetrating and removing biofilms and is ineffective against amoebae (often a host of Legionella).
  • Chlorinated water has an unpleasant taste.
  • Even at low dose levels, chlorine is irritating to nose, throat, and skin.
  • When mixed with acids, it releases toxic chlorine gas, and it can aggravate asthma.
  • When it reacts with organic matter it creates TCM and THM, cancerogenic substances for humans and animals.
  • Chlorine is corrosive to metals.
  • When pH is higher than 7.6, its efficacy is rapidly decreased.
  • It requires neutralisation before disposal, otherwise it is toxic to aquatic life.

How about silver ion?
Silver ion electrodes systems and liquids are effective disinfectants, however they are very expensive and can be rendered ineffective in water, high in chlorides such as we have here in Mallorca. The test equipment for this type of dosing to ensure effectiveness is also very expensive and should be factored into the initial purchase.

Benefits of stabilised hydrogen peroxide
MTSea Water system has the right solution for all these problems: it is a hydrogen peroxide based product called EndoSan, stabilised with silver ions.

This product:

  • Is effective at penetrating and removing biofilms.
  • Is a powerful bactericide, killing viruses, spores, fungi, algae and amoebae.
  • At dose level, it causes no irritation to the nose or throat.
  • Doesn’t release toxic gases and doesn’t produce TCM or THM.
  • Is completely biodegradable, once it has done its job, it degrades into water and oxygen.
  • Is non-corrosive at dose rates.
  • Is effective at a wide pH range, and stable and effective at a wide range of temperatures.
  • Doesn’t require any neutralisation at dose levels, before release.




For more details Tel: +34 971 230 771
e-mail: [email protected]
or visit www.mtseawater.com