By: William Jackson
Submitted: 2010-12-03 07:06:53 | Word Count: 595
As with any other organi
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sm, Legionella bacteria require a source of food / nutrients to grow efficiently and divide to sufficient numbers to colonise a water system. This can be provided in a number of ways; scale, rust, sludge, silt and even other organic matter such as amoebae. Indeed, recent evidence has suggested that the presence of other bacteria, common in complex water systems at outlets, can both hinder of facilitate the growth and proliferation of Legionella bacteria. That aside, tank cleaning and disinfection of water systems forms a critical part of managing the risk of water systems and general hygiene. One common misconception is that stored water systems should be cleaned and chlorinated on an annual basis. In a large number of cases this infact not required and can prove to be costly, time consuming and disruptive to the site and personnel involved. With reference to ACOP L8 (Approved Code of Practice for Legionnaire’s Disease) water systems should be cleaned ‘when routine inspection shows it to be necessary’ and in addition to this, where there is reason to suspect there has been some form of contamination or intrusive work has been completed on the plumbing system. These recommendations for tank cleaning would usually come from routine 6 monthly tank inspections. So, where does the thought of annual tank cleaning come from? This is actually a suggestion made by the DWI (Drinking Water Inspectorate) that does not form part of the Legionella guidance and only relates to where water is stored for consumption i.e. is of potable quality. In general, and suggested in the Water Regs, it is not advised that stored water is used drinking purposes, where possible this should taken directly from a mains supplied outlet. However, stored water can be consumed if; 1. The cistern meets all the Water Regulations (including the old By law 30) e.g. insect screen fitted, sealed lid, insulation and screened cistern breather. 2. Is sampled at least on a six monthly basis for bacteria, usually TVC, e-coli & coliforms 3. Is drained, cleaned and chlorinated to BS6700 standards on an annual basis Taking the average water system, where kitchen and drinking water outlets are taken directly from the mains, and tanked water is used simply for toilet flushing, hand washing and showering then tank cleaning may only be required every 3-5 years dependent on turnover, silt content etc. The above is becoming more and more important for large new builds where all site water is provided by means of a break tank and then passed through a booster set. There may of course be other mitigating circumstances or specific risk assessment recommendations that require a greater frequency of tank cleaning e.g. history of positive samples / biofilm in old pipework, but annual tank cleaning should certainly not be the default position in the absence of any of the above. One other issue not addressed above is that where site personnel are known to consume water from non-potable outlets where a fresh mains supply is available – in this instance a decision would need to be made by the Duty Holder. One way to mitigate this risk is the provision of suitable signage above the outlets which can save considerable money in the long run. For more information on tank cleaning and water system disinfection, please visit our website www.nemco-utilities.co.uk
Author Resource:-
Charles has been working with the various facets of legionnaire's disease for some time now and has a wide expertize on the same. He shares his insights with the readers through his scholarly articles.
