Ensuring that drinking water supplies, both at berths and piers and on board ships and aircraft, are safe to drink is the responsibility of the Local or Port Health Authority. Potable water can be taken on board a vessel when in dock or can be made on board using desalination techniques. Where desalination techniques are employed it is recommended that the equipment is not used within 20 miles of any land or other pollution source. In both respects the water on board the vessel should be wholesome and comply with the International standards for drinking water.
Contamination may occur during tank filling operations or during tank inspection. Hoses used for filling operations must be exclusively used for this purpose. They should be durable with a smooth impervious lining and have suitable adapters and caps. Contamination of the hose by dragging the ends on the ground, pier or deck or by dropping in to the harbour water must be avoided. Hoses and hydrants must be flushed through before connection to the tank filling point. Hoses should always be cleaned, capped and suitably stored between uses and should be disinfected every 6 months using superchlorinated water at 100 ppm with a contact time of 1 hour.
Tanks and distribution systems should be designed to prevent contamination and facilitate cleaning and disinfection. Fresh water tanks should be emptied, flushed and refilled every 6 months and opened, emptied, ventilated, inspected and recoated annually. During inspection and maintenance of the tanks care must be take to avoid the introduction of contaminants. Before refilling the tanks, the distribution system should be superchlorinated to 50 ppm with a contact time of 24 hours. In exceptional cases the concentration can be increased to 100 ppm with a contact time of 1 hour, however the system must be completely drained and thoroughly flushed before filling with potable water.
Further information is contained within, Merchant Shipping (Provisions and Water) regulations 1989, and Merchant Shipping Notices; M1214(1986), M1401(1989), M1373(1989) and M1375(1989).
All masters are advised to keep a 'Fresh Water System Maintenance Log' which should include details of: tank capacities, distribution system, filters, construction materials, maintenance schedules, disinfection schedules, sample frequency, sample results and remedial actions taken.
The most commonly used compounds for disinfecting drinking water are:
Powders - Chlorinated Lime and High Test Hypochlorite
Liquids - Commercially prepared Sodium Hypochlorite solutions
These chemicals are potentially hazardous and should always be stored, handled and prepared in accordance with manufacturer's instructions.
The chemicals are mixed to produce a chlorine releasing solution of known concentration. This solution is added to the ship's almost empty water tank. The tanks are then refilled with clean fresh water and all taps and outlets on the distribution system opened until they discharge chlorine smelling water. The system is then topped up with fresh chlorine solution to replace the water lost when draining off. The system is then left to allow a contact period of between 1 and 24 hours depending on the concentration of the chlorine used.
Following treatment the system should be drained of super chlorinated water and refilled with fresh potable water from a known clean source. The replacement water should have a residual free chlorine level of 0.2ppm.
APHA/HPA report - The Microbiological Quality of Water on Board Ships
Guidelines For Water Quality On Board Merchant Ships Including Passenger Vessels- Health Protection Agency Publication £6.00
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