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In a ship with a Surgeon the responsibility is delegated to him; although it is usual for the
ship to keep a detailed record of the amounts and timing for the addition of chemicals to each
tank as it is filled. In a ship without a Surgeon and in which only a stabilised bleach is used,
the Common practice is to follow the instructions in the Ship Captains' Medical Guide. In British
ships each tin of chloride of lime holds a measure and this (one-eight of an ounce) is considered
sufficient to purify 200 gallons of water. If the bleaching powder has 33% available chlorine,
this represents a dosage of rather more than one part per million.
Where water is taken "direct" from a town mains regarded as pure, there is no further chlorination
and rarely any subsequent check for free chlorine. Water taken from any other ports, or
from a barge in any port is viewed with suspicion by some shipping companies and is chlorinated.
It is tested four or five days later for the presence of free chlorine.
Filtration. This is commonly, and unlike shore practice, the last treatment. It is done in the
first stage of distribution. Patent filters are used with elements of carbon or other material that
can be "backwashed" or replaced as necessary. There is rather a tendency to neglect the filters.
This is possibly based on the principle that the water is pure anyway. The filters can then become
an incubator for bacteria which only cause anxiety when discovered by sampling during an
appropriate investigation of the water supply.
Distribution
Method. The distribution of water in ships is very varied in detail, but has to comply with the
principle that each "class" of supply — potable, domestic, fresh and salt — must be kept entirely
separate at every point. This might be considered, theoretically, to make the separation of potable
and domestic fresh water acceptable but it does, in practice, create problems. However good
the original design and installation, these standards can be difficult to retain when structural
alterations are effected in parts of the accommodation, possibly on several occasions. The pipe
lines can then become very complicated and may even become cross-connected as found aboard a
ship while an outbreak of typhoid fever was being investigated.
There is also the opportunity that the dual system gives for human error in operation and now
that the maintenance of all fresh water at potable standard is becoming the rule rather than the
exception, it is natural to assume that it is always so. Labelling of taps is apt to be an ineffective
substitute.
In accordance with the principle of separation the Regulations specify that when service
tanks are used they shall be directly connected with the main storage tanks for that class of water,
and that in ships of 1,000 tons or over the pumping shall be by mechanical means (ships of 3,000
tons for drinking water.)
When all the fresh water is maintained at potable standard it is possible to instal one distribution
circuit to cater for all the selected services. The terminal supply may be maintained by
a circulating pump and gravity feed tank in closed-circuit or preferably by a later method which
consists of a pressurised storage tank from which the distribution to terminals throughout the
ship is supplied at constant pressure. This principle of a common closed-circuit reduces the risk
of contamination, but, should it ever occur, the entire network of distribution will become involved.
There are numerous Regulations and more recommendations regarding the type and placing of
taps. Also the scale of provision of wash basins, baths and such like. There is no great present
concern with these, and it is not proposed to catalogue them here although it may be worth mentioning
that the supply of salt water to baths and showers is restricted to those provided in excess
of the scale.
Hot Water. The arrangements for hot supplies are not likely to produce direct hygiene problems
but calorifiers are subject to recommendations regarding siting ventilation and safety valve. When
exhaust gases from engines are used to heat water there must be alternative arrangements for use
in port.
Cooling. A cooled supply of drinking water must be provided in ships of 1,000 tons or more
going to foreign parts. A recommended method of cooling is to include a 20 gallon tank in the
refrigerated vegetable room, with draw off taps on deck and in the main pantry. An alternative is
to have a cooling coil in the tank using circulating brine.
Items of indirect distribution.
Drinking water in life boats. Although wooden casks are still to be found, galvanised steel
tanks are now more generally fitted. They should be, and usually are, frequently emptied, flushed
out and replenished. At longer intervals they are scrubbed out, if possible, and/or treated with
steam.
Drinking water bottles. These are still a compulsory piece of equipment in sleeping accommodation,
but it is obviously very difficult to ensure that they are all regularly cleansed and replenished.
Ice. For table service and drinks ice is made in the ordinary domestic manner. Drinking water
in divided trays is placed in a refrigerator. Made from a safe water it presents no more hazard
than any other "handled" ingredient of food or drink.
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