The provision of water on board vessels has changed little over the years. Fresh or potable water can be taken on board whilst a vessel is in port and stored or potable water can be made on board using desalination techniques. Single distillation equipment has been documented since the 1700’s however today high/low pressure evaporation, distillation, filtration or reverse osmosis techniques are used. A combination of desalination and the storage of water may be employed.
Factors affecting water quality include:
It is a requirement of the International Health Regulations 2005 that every port is ‘provided with a supply of pure drinking water’. 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.
Water quality standards specifically relating to water on board vessels are given in the HPA guidance on water quality on board vessels. If a microbiological examination of water reveals levels in excess of the standards shown in Table 3 then the water should be treated – the tank should be emptied, cleaned and refilled with fresh chlorinated water.
The UK generally accepts chlorine as a disinfectant which requires around 20 minutes contact time to react. It can be the case that shore mains water only contains low concentrations of free chlorine which may be further decreased within the ship environment. Although there is no requirement to do so and control measures will be influenced by the quality of the source water, it is considered good practice to add chlorine as a routine when loading fresh water to a level that produces a 0.2 mg/L (ppm) residual free chlorine or 1.0 mg/L (ppm) chloramine when chlorinated water is supplied. Some other treatments available include: Silver Coated Filter Candles, Electro-Silver Ionisation, Ultra Violet Sterilisation and Thermal Disinfection.
(information extracted from The Association of Port Health Authorities website)