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necessary. The decision for this lies with the Master or his Mate on watch, but the operation is
carried out by the Engineer on watch. The fittings are usually of a kind that require the use of a
spanner to reverse an inserted blank, so that accidental filling of fresh water into sea water
ballast is most unlikely.
There is a recommendation that tanks used for water ballast taken from the open sea should
not be used for storing potable water unless they have been cleansed. This is an ideal, and where
there is quick turn round in port, it may only be possible or expedient to flush out the tanks with
fresh water, especially at intermediate ports. A more serious danger lies in the reverse procedure
in which ballast tanks that have never been cleansed are used for fresh water. Some time ago a
Port Health Inspector in London, paying a routine visit to a ship, heard a complaint from the crew
that the drinking water made them feel sick (produced nausea). Enquiries revealed that as the
forthcoming voyage would normally involve the taking of water in ports where it was very costly,
an attempt had been made to effect an economy by pumping out the double bottom ballast tank and
filling it with fresh water. Fortunately for the crew this tank was put into immediate service before
the ship sailed.
Quantity
Drinking Water. The Regulations simply refer to tanks of adequate capacity, but the Merchant
Shipping (Seaman's Provisions) Order, 1957 lays down a scale of 28 quarts per man per week.
More simply a gallon a man a day.
Fresh Water (other than drinking water)
The Regulations specify that the tanks for fresh water to supply "washing accommodation"
shall have a capacity of at least 10 gallons for each member of the crew for each day likely to
elapse between successive replenishments. There must also be an adequate supply of hot and
cold fresh water to the laundry facilities and to a sink in the galley for washing-up purposes. No
separate amounts are specified, so presumably this must be part of the 10 gallons.

With no reason to believe that the requirements at sea are now any less than ashore for the
same purposes, the total of the 4 starred items plus waste 15 gallons must be the minimum for
fresh water, and preferably this should all be of potable quality.
In practice the shore consumption for all purposes now exceeds 50 gallons per head per day
in the area supplied by the Metropolitan Water Board. Similarly, at sea, in ships which are able
to maintain an almost unlimited supply of fresh water of potable standard for all purposes except
W.C's. the average consumption just exceeds 40 gallons per head per day.
Some idea of the storage problem may be obtained by considering an actual case. A ship
with a total complement of 600 and a maximum of 10 days between ports carries 1,200 tons of
fresh water of potable standard, plus a separate 250 tons for the boilers, and is only just able to
maintain "unlimited" supplies.
Treatment
Effect of Storage.
In shore supplies storage is one of the most important factors in the self-purification of water.
It reduces the number of all bacteria and e.g. destroys about 90% of typhoid in five to seven days.
This is not important, or indeed revelant, in relation to ships supplies where the aim is to store
pure water and then prevent it from becoming contaminated.
The tanks in which water is stored vary considerably in shape and size, but generally hold
at least 40 tons and have a minimum depth of 3 feet, even in double bottom tanks. They are adso
normally totally dark and filled to capacity. Thus, provided the cement washing or other "lining"
is effective there is no reason for any abnormal growth of bacteria. It conforms, in other words, to
the established principle that once a water has been pumped it should never be allowed to see the
daylight until it issues from a consumer's tap.
Chlorination. When this is decided, it is customary to introduce the chlorine before filtration.
Since this is normally only done with doubtful supplies, which could contain much suspended
matter chloramination is to be preferred.
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