CLEANING OF WATER TANKS AND CONTAINERS FOR MOTORHOMES (RV s), CARAVANS AND BOATS

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1 DRINKING WATER TANKS & CONTAINERS Introduction This article advises on cleaning and disinfection of drinking and grey (waste) water vessels housed within Motorhome s, RV s, boats and containers commonly used in caravanning and camping. Why Disinfect? All water in the UK (and most European) Countries contain a small residual (0.2mg/l) of Sodium hypochlorite (chlorine) to prevent secondary infection, so why clean and disinfect? Sodium hypochlorite (chlorine) comes out of solution as a gas very quickly once it has left the water main. Water left standing in a tank or container will soon lose the small residual amount of chlorine leaving the water open to infection. How soon will depend on the temperature and whether the chlorine has to combat any infection it comes into contact with, when that happens the chlorine is used up right away. Biofilm Left untreated the bacteria populate the surfaces of tanks and pipes and develop into a biofilm, typically a brown or green coloured slime, where they live and multiply. Mittelman (1985) reported that the development of a biofilm can take several hours to several weeks to develop. The indication of slime in water tanks (sometimes accompanied by an earthy or vegetable smell) probably means that cleaning has not been done effectively in the past, or it is in need of being done. Coglan (1996) referred to it as Slime City built by the microbes where nutrients are passed to and fro along channels like highways for the bacteria to develop and thrive. Mittelman (1986), after considering a range of biocides,reported that "Chlorine is probably the most effective and least expensive of all oxidizing and nonoxidizing biocides." The activity of chlorine against attached biofilms is particularly high; not only are planktonic and biofilm bacteria killed, but chlorine also reacts with and destroys the polysaccharide web and its attachments to the surface. By destroying the extracellular polymers, chlorine breaks up the physical integrity of the biofilm. Most common waterborne pathogenic bacteria are typhoid, cholera, E.coli, campylobacter, salmonella norovirus, are present in most all untreated surface waters. Disinfecting will also remove viruses, moulds and algae which can also develop over time if the vessels are not used. Some types of infection called Oocysts are highly resistant to the residual chlorine dose found in mains water and can only be eradicated by higher doses of chlorine and flushing.. They are found in most animals and in the ground so any contact with the ground can risk introducing them to the water container. There are two main types of oocyst; Giardia Lamblia and Cryptosporidium once introduced to water, can survive for weeks, even at low temperatures and if ingested cause sickness and diarrhoea which can also last for weeks. There is no known cure and recovery is down to the person s immune system and management of diet, the elderly, sick and children are worst affected. Following simple hygiene rules and disinfecting vessels regularly (at least once or twice a year) will help in the prevention of secondary infection by either oocysts or pathogens: Always keep tanks and containers closed* at all times to prevent airborne infection entering (flying insects; flies, mosquitoes, gnats, lace wings and also crawling insects such as spiders beetles, lice etc.) Never rest the drinking water cap or hose ends on the ground where it might become infected wash them under a running tap or use a bleach spray or wipe. Ends of hose connection taps and hose pipes can also be disinfected with bleach spray or wipes. *The Water Regulations for storage cisterns state: When an installation is intended to provide wholesome water it must comply with Clause G16.13 of the Government Guidance viz.: Cisterns storing water for domestic purposes should be watertight and, where required, be lined or coated with a suitable impermeable material; they shall be provided with warning and overflow connections, as appropriate, which are so, constructed and arranged as to exclude insects. They should have a rigid, close fitting and securely fixed cover which is not airtight but which excludes light and insects from the cistern. Although vessels in motorhomes are not covered by the regulations, it is the guiding principle of preserving water quality by keeping vessels closed and eliminating infection from airborne infection and insects, that is relevant. Page 1

2 Disinfection It is critical that the disinfection process is carried out at the right strengths and contact times to be effective on one hand and to prevent taste problems on the other. It is difficult with some disinfection products to actually work out the precise dosage rate. Having many years experience in the disinfection of water systems, I prefer to use Rapid Release 1000mg/l Tablets which contain 1 gram of free chlorine or 1000milligrams per litre in 1 litre of water. They are in tablet form and are relatively safe for storage, very cost effective, and will not degrade if kept dry and are accurate when measuring the strength. Almost any of the other proprietary products can be used but the important bit is to identify the strength in milligrams per litre or parts per million (both the same) as this makes it easy to get the right concentration. I never use household bleach because most of them contain surfactants which may be detergent based. Surfactants are added to facilitate surface wetting and break down fats and grease prevalent in household cleaning. It may be more difficult to completely flush them out and could lead to taste problems. Procedure for Drinking Water Tanks How Many Tablets? The Rapid Release 1000mg/l Tablets: 1 tablet makes mg/l or parts per million (both the same) concentration. We need 20/25 mg/l (ppm) standing for a period of 1 hour minimum and 2 hours maximum this dosage rate is for average situations where the tank is relatively clean and well maintained, if the tank is has not been cleaned for a long period then it may necessary to increase the dosage or extend the contact time please contact if you need advice on this aspect. One tablet in 1 litre solution will disinfect 1000/20 = 50 litres of water at 20mg/l, or 1000/25 = 40 litres at 25mg/l Many on board tanks are of the order of 80litres or 18 gallons. So, 2 tablets will do 100 litres at 20mg/l (ppm) or 80 at 25mg/l. It does not have to be that precise, if the concentration is stronger the contact time can be less and if weaker leave longer but never longer than 2 hours. I always stick to the 2 hour maximum because it is possible that if left longer the sodium hypochlorite may leech into the plastic material and cause a taste reminiscent of TCP. If you want to work out the exact number of tablets use the following formula: (Capacity of your tank x strength (20m/l))/1000 = Number of 1000mg/l tablets, or use the following table. The procedure is very simple and safe if you follow a few basic rules: DRINKING WATER TANKS & CONTAINERS NUMBER OF TABLETS REQUIRED FOR 20mg/l CONCENTRATION Capacity in Litres Capacity in Gallons Number of Tablets Round tablets up to nearest whole number and reduce contact time (MIN 1 HR. MAX 2 HRS) (Any volume of tank can be calculated for the number of tablets required) Instructions (Included): 1. If the system has been drained down for the winter you will need to fill the system first; this ensures the hot water tank is full, and prevents any solution entering the hot water tank. (Truma do not recommend chlorine based products for their systems) 2. With enough room in the cold water tank to allow mixing, put the required amount of tablets into the tank (or container) through the filler cap and fill to the brim including the filler pipe with fresh mains water. (if you can t fill to the brim due to the tank having an overflow see article; Cleaning The Drinking Water Filler Pipe in Motorhome s) 3. Leave to stand for a minimum of 1 hour and a maximum of 2 hours dependent upon the strength. Page 2

3 4. After 1 to 2 hours, open the cold water taps and draw some of the solution through the cold taps and leave for about 15 minutes, which will combat any infection in the pipe work. (There is little risk to pumps and seals at this strength, in fact Shurflo recommend sterilising with bleach in their installation instructions. If you have a stainless steel sink ensure that the contact time is as short as possible and the solution is flushed away with fresh water). 5. After 15 minutes drain the remainder (or empty the container) via the drain tap on the tank or via the cold taps into the grey water tank and then flush the tank for a few minutes with the hose pipe. (Note: if you are cleaning the waste tanks at the same time you can add the extra tablets as described below for Grey Water Tanks). 6. Refill the fresh water tank (or container) and thoroughly flush through the system and you are done; with a clean and bacteria free tank and system. 7. For the hot water system simply ensure the hot water tank is full, heat up to maximum temperature for a minimum of 1 hour and flush for a few minutes through the taps. (Truma do not recommend chlorine based products for their range of hot water systems) Should you detect any taste problems then re flush and refill the tank and it should disappear. (Chlorine comes out of solution over time, sometimes if you get a TCP taste from mains tap water then fill a jug or bottle leave in fridge overnight and there will be no discernible taste.) Frequency of Cleaning How often should you clean the tanks? This is a question often posed, it this all depends on usage factors and also temperature. Drinking water that is allowed to stand at 18/20 deg C will give the right conditions for bacteria to develop and grow including legionella. The more often the motor home is used the less likely it is that the drinking water tank will need to be disinfected, but the more the grey water tank will need attention and vice versa. Here is a regime that I follow it is not rigid by any means and as stated above it is possible for a biofilm to develop in hours to weeks but I think this is a good average. DRINKING WATER TANKS FREQUENCY TREATMENT (see 1 to 2 Weeks inactivity Flush out with clean water and refill 3 to 6 weeks inactivity Dose with half strength solution) 10mg/l) for about an hour flush out via tank drain off and next tank through system. Refill or top up. Over 6 weeks and at least once a year. Full treatment (20mg/l for 1 to 2 hours), flush out via tank drain off and next tank through system. Refill or top up GREY WATER (WASTE) TANKS The build up of organic matter in the Grey water tanks can lead to unpleasant smells ( bad eggs ) and can be treated in the same way to kill off the bacteria causing the problem. For this I would use a strength of 50mg/l (double that of drinking water tanks) and double the contact time to 4 hours. With liquid bleach there is always a danger of spillage, with resultant damage to whatever it comes into contact with. Some metal sinks will not tolerate neat bleach being poured into them, but a tablet placed on the sink outlet whilst the tap is running alleviates any risk of damage as the sodium hypochlorite is being diluted all the time. The tablets are more convenient, easy to store, always on hand, have a longer shelf life, safer, and avoid the need to carry liquid bleach with its inherent dangers. Strength The strength and contact time is not as critical as for that as drinking water tanks as there will be no risk of taste problems etc. Both are doubled for that of drinking water tanks as there will be more organic and bacterial deposits from the grey water (see table below). GREY WATER TANKS & CONTAINERS NUMBER OF TABLETS REQUIRED FOR 50mg/l CONCENTRATION Capacity in Litres Capacity in Gallons Number of Tablets Page 3

4 Round tablets up to nearest whole number and reduce contact time (MIN 2 HR. MAX 4 HRS) Procedure for Grey Water (Waste) Tanks 1. Work out the number of tablets for the capacity of waste tank. 2. Place the tablets one at a time in one (or more) of the outlets. 3. Turn on tap(s) as the tablet(s) dissolve, add further tablets until all are dissolved. 4. Fill tanks to maximum 5. Leave for 4 hours 6. Empty out to drain and flush. Frequency As for drinking water tanks this will depend on the usage of the motor home, except in this case the more the frequent the use the more likely the tanks will need cleaning. GREY WATER TANKS ORGANIC FREQUENCY TREATMENT DEPOSITS (Actual Usage) (see Light 6 to 8 weeks Half strength treatment (25mg/l for 4 hours or 50mg/l for 2 hours) Medium 4 to 6 weeks Full treatment (50mg/l for 4 hours) Heavy 2 to 4 weeks Full treatment (50mg/l for 4 hours) Safety The strength of the solution is not normally considered hazardous as long as the dosage is adhered to. Household bleach is normally <5% (50000mg/l) which is up to 2500 times stronger! The procedure is very simple and with care no problems should be encountered, however a few safety notes: Remember all products of this nature are mild bleach and so can be harmful to special surfaces, clothes, carpets, lawns, etc. and is corrosive to metals. Contact with acids liberates toxic gas Can be irritating to eyes and skin Dilute when flushing to drainage system Always keep products of this nature out of the reach of children Don t store made up solution in bottles or containers (it may be mistaken for mineral water) Accidental spillages should be flushed away with water. First Aid Splashes to eyes should be irrigated with water for five minutes and Wash off skin with water or wear protective gloves. If swallowed drink lots of water don t get the person to vomit as this makes it worse, seek medical assistance. Page 4

5 CLEANING OF WATER TANKS AND CONTAINERS FOR Always follow manufacturer s instructions Storage: The shelf life is about 3 to 5 years if kept in a cool, dry, safe place, seal the bag after use with the tie or a knot (if possible store the bag in a small plastic sealable container correctly labelled). Page 5

6 Cost The Rapid Release 1000mg/l tablets are very economical. A 100 litre drinking water tank costs about 1 to treat and 2 for a similar size grey water tank. Please Note: I can supply a pack of 10 Rapid Release 1000mg/l 10 tablets for 5.49, (treats 500 tablets 9.99, 30 for 13.99, or 40 for inclusive of delivery by Royal Mail first class post (UK Mainland only) and full instructions. Please visit the shop ( if you want to order. Page 6