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Notice to Shipowners, Masters, Fishing Vessel Skippers, Shipbuilders and Repairers
This notice supersedes Notices Nos. M.410, M.633 and M.901

  1. Recently acquired scientific evidence indicates that closer attention needs to be given to the quality of freshwater in ships' storage and distribution systems in relation to the growth of various potentially dangerous bacteria, including Legionella or to the presence of toxic chemicals.
  2. The relevant United Kingdom Regulations which apply to freshwater on board ships are:

    The Merchant Shipping (Crew Accommodation) Regulations 1978 SI 1978/795. The Merchant Shipping (Crew Accommodation) (Fishing Vessels) Regulations 1975 SI 1975/2220. The Merchant Shipping (Provisions and Water) Regulations 1972 SI 1972/1871. The Merchant Shipping (Provisions and Water) (Fishing Vessels) Regu­lations SI 1972/1872.

    Food Hygiene (General) Regulations 1970 (which apply only to vessels plying exclusively in inland waters or engaged exclusively in coastal excursions solely on the coasts of Great Britain but not foreign voy­ages). The Public Health (Ships) Regulations 1979 SI 1979/1435.

  3. The Merchant Shipping (Crew Accommodation) Regulations 1978, Regulations 29(3), 30(2) and the Merchant Shipping (Crew Accommodation) (Fishing Vessels) Regulations 1975, Regulations 26(2), 26(6), refer to requirements that the supply of drinking water shall be so arranged and constructed to prevent any risk of contamination, and in the former regulations that the supply of washing water shall be so arranged and constructed to minimise any risk of contamination. Most dangerous waterborne bacteria affecting humans are ingested in drinking water but significantly Legionella bacteria can gain entry to the respiratory system from washing water suspended in air in the form of a fine mist as created by shower or tap sprays. Consequently this means that former distinctions between the standards required for drinking and washing water should not be maintained. Additionally, revision of the advice given in the Ship Captain's Medical Guide 21st edition has become necessary, see also Notice No. M.1216.

  4. The following principal features should now be carefully considered to ensure the supply of wholesome freshwater on board ships which is bacteria free, bright, clear, and virtually colourless.


    4.1.1 Freshwater obtained from shore mains supply or water barge- This should be transferred by a hose exclusively used for that purpose. Hoses where carried on board ships should be suitably marked and should be stowed in a position clear of the deck where they are not subject to contamination and should always be capped at both ends after being drained off following their use. Fresh water hoses should be flushed through before each watering commences and discharged to waste.

    4.1.2 Routine treatment of freshwater-Shore mains water in the United Kingdom normally contains only a very low concentration of free chlorine and the ship environment decreases this further. In foreign countries there may be no free chlorine content at all. All freshwater taken from shore or water barge (subject to 4.1.4 below) should therefore be chlorinated on loading to a sufficient concentration to ensure a residual free chlorine content of 0.2 ppm.

    This concentration may be achieved by the traditional manual method using the revised formulae given in the Ship Captain's Medical Guide per Notice No. M.1216 or by using an automatic chlorination unit in the ship's deck filling line. The concentration may be checked by means of a Lovibond comparator kit.

    4.1.3 Freshwater from low pressure evaporator or reverse osmosis plant- Water from such plants should in general only be produced when the vessel is at least 20 miles from land or remote from any risk of estuarial pollution which in some sea areas can extend well in excess of 20 miles from land. The sea water suction to evaporators or reverse osmosis plants should be separate from other sea suctions eg machinery cooling water inlets, fire pump suctions, etc and sited forward and on the opposite side of the ship from sanitary or bilge discharges. It is important to note that any chemical used in an injection system to a sea suction intended to prevent the growth of organisms in the ship's piping system serving water making apparatus should only be of a type spec­ifically approved by the Department for that purpose. It is a condition of the Department's approval and fitting of low pressure flash evapor­ators or reverse osmosis plants on board United Kingdom registered ships that the constraints described are closely observed. All water-making plants producing freshwater from seawater require to be fitted (subject to 4.1.4 below) with an automatic chlorination unit and although formerly the Department has been prepared to grant exemption to allow an ultra-violet sterilizer unit to be fitted in lieu of the auto-chlorinator unit this policy is now discontinued. Ultra-violet sterilizer units will continue to be accepted as a supplementary sterilization system in both new and existing ships but an auto-chlorination unit (subject to 4.1.4 below) will be required in new ships in accordance with the Regulations. In existing ships already exempted on the grounds of an ultra-violet sterilizer unit being fitted a regular routine for the chlorination of freshwater tanks to maintain 0.2 ppm concentration should be established similarly to ships obtaining their water only from shore or water barge. (See Notice No. M.1216).

    4.1.4 An equivalent alternative means of sterilising fresh water similar to the chlorination method will on submission be considered by the Department on its merits.


    4.2.1 Storage tanks and delivery system intended for drinking or washing water-These should be independent of any other services wherever possible. Where there is no alternative supply to other services requiring freshwater, eg machinery jacket water, oil purifiers, or a freshwater WC flushing system it is preferable that there should be a clear air break in the freshwater supply pipe to any such system or tank. If in turn this is impracticable it is essential that the supply pipe is provided with an efficient non-return valve and a vacuum breaker or back-flow preventer. Where freshwater is to be used for flushing water closets either a vacuum breaker should be fitted between the flushing valve and the water closet or a suitable type of cistern should be provided.

    4.2.2 Siting of tanks-Tanks intended for drinking water should nor­mally be sited above the inner bottom and independent of the hull but tanks other than peak tanks (which are difficult to clean) not independent of the hull may be utilised if they are of all welded construction and suitable in all other respects. In particular all freshwater tanks should be so sited and be of such dimensions that they are readily accessible to facilitate inspection, cleaning and coating. In small ships of less than 2500 GRT where the use of an aft peak cannot be avoided particular attention should be given to filling and smoothing the bottom recesses in the tank with cement or other suitable non-toxic composition. Fore peak tanks which by nature are much more susceptible to damage should not be used. In ships with only one freshwater storage tank sited in the double bottom an alternative reserve drinking water tank should be provided for use in emergency.

    4.2.3 Construction-The internal structure of all freshwater tanks should be designed to ensure efficient drainage through adequate limber holes to the suction and in general continuous welding should be used. No freshwater tank should have a common boundary with a tank containing oil or any other liquid except clean water ballast. During con­ struction or repair or at dry-docking or slipping, at intervals not greater than 5 years, it is important that a pressure test of all freshwater tank boundaries including the outer shell of a ship where this applies should be conducted to ensure that there is no seepage into the freshwater tanks from the sea or adjacent water ballast tanks. Manhole accesses to freshwater tanks should be of adequate size and sited clear of possible sources of contamination. Manholes sited in tank crowns should be fitted with raised coamings. No piping other than piping containing freshwater of the same standard as the tank contents should pass through a freshwater tank. WCs, laundries or any other feature likely to contaminate freshwater should be sited clear of the crown of freshwater tanks. Air, filling, and where practicable sounding pipes, should stand sufficiently high above the deck to prevent fouling. Air pipes should be of the swan neck type fitted with a wire gauze and should be sited in a protected position where the entry of sea water on deck is prevented. Sight glasses or gauges should be provided where practicable to indicate the water level in the storage tanks in order to avoid as far as possible the use of sounding rods.

    4.2.4 Coatings-Freshwater tank structure when new should be thoroughly wire brushed, scrubbed and primed before coating with cement wash or a proprietary coating system and should be thoroughly aired before filling. When coating systems other than cement wash are used such as modern epoxy finishes specially developed for freshwater tanks it is essential that the coatings are applied and allowed to cure strictly in accordance with the manufacturer's instructions otherwise the water can subsequently become unfit for use. The manufacturer's advice on filling, flushing and emptying freshwater tanks before these are connected to the distribution system should also be strictly adhered to.


    4.3.1 Water treatment, filters, mineralisers, softeners, etc-All sea water drawn by an evaporator or reverse osmosis plant should be passed through suitable sand filters before being introduced to the water making apparatus and all water produced by such plants in new ships must be disinfected by an autochlorination unit or equivalent (per 4.1.4 above) before it is pumped to the storage tanks. An auto-chlorinator for this purpose may if desired, and if of sufficient capacity, have a connection to provide the same facility for the deck filling line. If it is considered necessary to neutralise the pH value of the product water or to make the water more palatable it is preferable that such a neutraliser or mineraliser be inserted between the water-maker and the auto-chlorinator and therefore before the water is passed into the storage tank.

    4.3.2 Freshwater distribution pumps-These should be dedicated to domestic freshwater services only and should not be capable of being connected to any other service, eg salt water.

    4.3.3 Calorifters, pressure tanks, etc- These should be designed where possible to avoid stagnant zones forming and should be fitted with efficient connections at the lowest point of the unit to ensure that all loose scale, or sludge can be completely drained off after cleaning and maintenance. Calorifiers should be provided with adequate access to enable scale deposits or products of corrosion to be removed and cleaning to be facilitated.

    4.3.4 Piping-Care should be taken not to run hot and cold water pipes adjacent to one another unless the pipes are adequately insulated to prevent transfer of heat from hot to cold lines.

    4.3.5 Overall design of freshwater systems-The fresh hot and cold water distribution systems should be designed to provide maximum circulation of the systems and to avoid deadlegs especially where temperatures could arise which might provide the optimum conditions for bacterial growth (ie 15°C to 50°C). This possibility increases as the size of the system increases when sections of the system are not kept in continuous use. Consideration should therefore be given in ships with accommodation for more than 100 persons to providing a ring main system with circulation pumps in both hot and cold water lines. The freshwater tanks arrangement in every ship should enable tanks to be used in regular rotation in order to avoid the problems associated with stagnation.

    4.3.6 Fittings and accessories-All items used in the construction of ship's freshwater plumbing systems should in future be of types that do not provide a habitat for bacteria, which can occur in the case of natural rubber, various plastics, and fibre accessories, or leach out toxic constituents. In line with the policy adopted by all Water Authorities in the United Kingdom (under the United Kingdom Water Fittings Byelaws Scheme) it is recommended that all materials used in freshwater systems should be of those listed in the current edition of the Water Fittings and Materials Directory (revised annually) prepared by the Water Research Centre, Henley Road, Medmenham, PO Box 16, Marlow, Bucks SL7 2HD, ie pumps. valves, "O" rings, seatings, compounds, pipes, shower mixers, taps, calorifiers and all other sundry items. When a vessel is constructed or refitted abroad fittings or materials validated by a local national agency to an equivalent standard may be acceptable if suitable documentary attestation is available. (See also paragraph 4.5 below).


    4.4.1 Freshwater storage tanks-It is recommended that these should be opened up, emptied, ventilated and inspected at intervals not exceeding 12 months and thoroughly cleaned, recoated as necessary, aired, and refilled with clean freshwater chlorinated to a concentrated of 0.2 ppm. The cleaning process should include disinfection with a solution of 50 ppm chlorine. In addition tanks should be thoroughly pumped out and, where necessary, hosed prior to refilling at approximately 6 month intervals.

    It is further recommended that tanks should be super-chlorinated at a concentration of 50 ppm for a period of not less than 4 hours and then completely flushed out and refilled at 0.2 ppm concentration at every refit or dry docking period.

    Persons inspecting or working in freshwater tanks should wear clean clothing and footwear which has not been used for any other work area, and should not be suffering from any skin infection or communicable disorder.

    4.4.2 Distribution system-The various elements of the freshwater production, treatment, and delivery system, ie sand filters, evaporators, reverse osmosis plant, auto-chlorinator, neutraliser/mineraliser, softeners, pumps, pressure tank, calorifier, carbon filter, ultra-violet sterilizer (where fitted), should be inspected, cleaned, flushed out, back washed, re-charged or items replaced where appropriate, in accordance with the makers' instructions. It is recommended that in complex systems a Freshwater System Maintenance Log be kept itemising each tank and each principle unit in the system. Alternatively the system should be itemised in the ship's Preventative Maintenance Work Programme where such a regime has been adopted.

    Some items of equipment require particularly careful and frequent atten­tion. eg filters on not less than a monthly basis to clean and where necessary change the media to ensure that the apparatus has not become contaminated by bacteria or other foreign matter. Calorifiers should be opened up and inspected scaled and cleaned periodically and before draining should be raised to a temperature of 70°C for at least 1 hour to ensure destruction of bacteria which may have colonised the lower and cooler zone of the unit. At every refit or dry docking period the whole delivery, tanks, and distribution system from machinery space to furthest outlets should be charged with super-chlorinated freshwater at a concentration of 50 ppm residual free chlorine and left for a period of 12 hours. After flushing through the storage tanks should be chlorinated to a concentration sufficient to maintain 0.2 ppm residual free chlorine.

    Shower heads and their flexible pipes where fitted should be thoroughly cleaned in a 50 ppm chlorine solution routinely every 3 months. Particular attention should be paid to fittings in toilet accommodation which may have been out of use for extended periods and these should also be so treated before re-use.

    4.4.3 Hoses-Disinfection of hoses should be carried out as a routine measure every 6 months, or whenever any contamination is suspected. Hoses should be thoroughly flushed through and completely filled with a solution of 50 ppm residual free chlorine which should then be allowed to stand for a period of at least 1 hour (see Notice No. M.1216) before the hoses are emptied and restowed.

    4.4.4 Chlorination-Guidance for the manual chlorination and super-chlorination of freshwater tanks as given in the Ship Captain's Medical Guide (as amended reference Notice No. M.1216) should be followed. It should be noted that as the chemicals used are oxidising agents and can be corrosive proper protective clothing including eye protection should be worn and the chemicals should be labelled and appropriately stored in accordance with the manufacturer's instructions.

    4.4.5 Corrosion and scale inhibitors-It is often the practice to add scale or corrosion inhibitors in the main or auxiliary engine jacket water used as the heating medium in low pressure flash evaporators. As there is a risk of minor leakage of such water into the flash side of the evaporator it is important that such inhibitors are of types approved by the Department.


    4.5.1 New ships- The freshwater systems in new ships should be care­fully designed installed and maintained in accordance with the principles set out in this Notice. In particular the arrangements should facilitate cleaning. Equipment and materials should be carefully selected from the current Water Fittings and Materials Directory or foreign equivalent in order to minimise potential contamination. Auto-chlorination is not a mandatory requirement in ships obtaining freshwater only from shore sources or water barge but this method should be considered as a more reliable means of chlorinating the ship's freshwater supply than manual chlorination.

    4.5.2 Existing ships-Where unsuitable materials may have been fitted to shower fittings or taps ie natural rubber or certain plastic hoses, washers, "O" rings, etc which provide conditions for bacteria to colonise, such items should be progressively removed in the course of normal maintenance and acceptable substitutes as listed in the Water Materials Directory or foreign equivalent fitted in lieu. It is essential that all parts of the fresh water system are maintained in a clean and hygenic condition as indicated in this Notice.

    4.5.3 All ships-The use of sea water in the preparation of food, washing of utensils, cleaning of galley equipment or in installations such as potato peelers should be avoided and only potable water should be used for washing down in food preparation or storage spaces. The ship's catering staff should be advised appropriately.

Department of Transport Marine Directorate London WC1V 6LP June 1986

© Crown copyright 1986