Good drinking (potable) water is essential aboard a ship and it is important to keep a constant eye on its quality. If you suspect something is the matter with the water, you must investigate the problem more fully.
Watch out yourself
The look, smell and taste of drinking water are three factors that you can watch out for yourself. If there is anything wrong with the water/system, it is vital that you are quick to notice and react.
Appearance
Water should be clear and not discoloured. Discolouration can be due to ochre (iron) or manganese dioxide. Lime deposits can make the water cloudy.
Smell
Water should smell fresh. A sweet, sickly smell is a sign of lack of oxygen which is often caused by biological processes that form ammonia and methane. A smell of rotten eggs comes from hydrogen sulphide. Contamination with chlorinated organic compounds can affect the smell of fresh water.
Taste
Temperature is important for taste. Water should feel cool, with a tap temperature preferably around 120C. Water should taste fresh - this is a sign of sufficient oxygen content. Water should not taste salt as this means that it contains chloride. A disagreeable taste and smell of rotten eggs or iron means hydrogen sulphide/iron contamination. Water should not taste bitter at all as this points to a content of magnesium sulphate which is also undesirable. There should be no disagreeable taste of hardness from calcium and magnesium salts. Finally, water should not taste of organic compounds such as chlorine/ phenols. Watch out if several crew get diarrhoea, as this can be a sign that the water is contaminated. If you have any misgivings about the quality of the drinking water, send a sample for analysis.
Analysis of drinking water
Drinking water analysis gives the bacterial content of the water. Below, there is a description of what such an analysis can reveal and what the figures mean.
Colibacteria, coliform bacteria 370C
These bacteria are not hazardous in themselves and have nothing whatever to do with defecation. But they are a sign that the water contains surface water which can contain bacteria that are dangerous. Finding coliform bacteria in a sample is taken seriously; new samples will be taken for testing and the system examined to find out where contamination is coming from. If the coliform bacterial count is high or if bacteria are present in a new sample, consider ordering drinking water to be boiled before consumption.
If the sample contains coliform bacteria, the water must also be checked for Escherichia coli (E. coli).
Escherichia coli (E. coli)
This group of bacteria originates from animal or human faeces and must definitely not be present in drinking water. As bacteria cannot survive long in water, it is always a sign of fresh contamination from waste or surface water containing faeces. Finding E. coli will mean a new water analysis and that all drinking water must be boiled before consumption.
Bacterial count at 220C
A high count is a sign that undesirable bacteria are present in the water and/or that the water is allowing bacteria to grow. If the figure is high, this is not in itself a health risk but does mean a new sample must be taken and the test results re-examined.
Appearance, smell and taste
In a drinking-water analysis, the laboratory also examines the appearance, smell and taste of the water.
What to do with the results of the analysis
If there are coliform bacteria in the water sample, check the water system for leaks. Any problems found must be fixed.
If there are E. coli in the sample, all drinking water must be boiled before consumption. The presence of E. coli means more dangerous germs may get into the water at any time. The system is vulnerable so the water supply system must be thoroughly checked and the source of contamination closed. The order to boil water can be cancelled when a new sample shows no bacteria are present.
If E. coli are identified in a sample, they may have already been present in the water for a short (sometimes a long) period. If you ask the crew, they will normally answer that their health is as usual but if asked directly, you will find that several of them have had diarrhoea.
A high bacterial count at 22oC may be due to water tanks not having been emptied or cleaned often enough. It could also be caused by recent work on the system. Finally it could be caused by contaminated surface water, which is why the entire water supply system needs checking to identify and fix the source of contamination.
Maintenance
It is important for the system to be properly maintained and to think carefully before carrying out any repairs on the system. This is crucial for drinking water quality. There have been several cases of cutting oil being found in the water after repairs or dirt from footwear from crew inspecting tanks. This lets bacteria grow in the water.
Disinfection of water aboard is not a good idea but can sometimes be required. If there is something wrong with the water, the system must be checked for leaks, etc. Other reasons for poor drinking water might be that breather pipes are blocked, insect screens are absent, that the tank needs insulating against sources of heat or that the tank has recently been treated/painted.
The latter requires a tank-cleaning operation. If you get water from ashore, consider asking the local authorities about water quality.
Contact your supplier if there are problems with a fresh-water generator, distillation plant, etc.
Disinfection
Only disinfect when water has been tested and you have identified the source of contamination. Consider whether you need to disinfect or whether it will be sufficient to flush the system. Flushing with lots of water is particularly effective, it is usually easy to do and is a good solution.
Disinfection usually means chlorination since this has several advantages. But as the aim is to neutralize the bacteria, in theory any bactericide will do. In practice, only silver (colloidal) salt is generally used instead of chlorination.
Different kinds of chlorine:
- Bleach (sodium hypochlorite) is a yellow/green liquid when fresh. It contains 140-150 grams of active chlorine per litre (15% active chlorine).
- Chlorinated lime is a more stable form of chlorine. When mixed with water, an insoluble residue can form so it must be mixed very thoroughly. It usually contains 30-35% active chlorine.
- HTH tablets 5 g. (Hydro-Tox-Hypochlorite) contain about 70% active chlorine.
Working with chlorine
Read the workplace instructions. There is a considerable risk of a serious accident if safety regulations are not observed. Chlorine is extremely poisonous so always follow the instructions in the safety data sheet.
You should never work alone when working with chlorine.
When disinfecting a drinking-water system, the water tank should be cleaned and washed down with a solution containing 500-1000 mg of active chlorine per litre. The piping system can subsequently be filled from the tank with a solution containing 50-100 mg of active chlorine per litre.
Fill the system with so much solution that water with a strong smell of chlorine runs from all taps. Leave the chlorine solution in the system for at least 3 hours, after which should still be a smell of chlorine when the taps are turned on. If not, repeat the procedure. Then turn on the taps and let the water run until the taste and smell are normal again.
After a couple of weeks, test for bacteria again. If something is still wrong, you must try to find the reason for the problem.
Legislation
Drinking (potable) water requirements
Drinking water requirements are given in the Environmental Protection Agency's Order on water quality and inspection of water supply systems - Notice No. 871 of 21 September 2001.
The requirements apply to ships calling at Danish ports. For ships calling at foreign ports, the rules are not quite clear but if the Danish rules are observed, this should be enough.
Drinking water tank requirements are given in Danish Maritime Authority Notices, Chapter B II-3 of 1 June 2001, Rule 20 Potable water systems, which states among other things that:
"Tanks should have the necessary manholes and they should as far as possible be accessible for both interior and exterior inspection. Tanks should be cement lined or cement-washed inside or have some other suitable lining. Breather and filling pipes for tanks should be led up to a reasonable height over the deck. The pipe openings should be so arranged that impurities cannot get into tanks."
Fresh water generators, distillation equipment or similar should be type approved.
Water quality requirements:
- Coliform bacteria must not be present
- Escherichia coli (E. coli) must not be present
- Bacterial count at 22oC. Recommended figure: 50/ml. Highest permitted value: 200/ml
- Try to ensure that water is at most 12°C at the tap