1. TANK CLEANING WORK
- BY NEMCO UTILITIES
(WWW.NEMCO-UTILITIES.CO.UK)

2. TANK CLEANING WORK
As with any other organism, 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.
For more information on tank cleaning and water system disinfection, please visit our website
www.nemco-utilities.co.uk

3. TANK CLEANING WORK
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.
For more information on tank cleaning and water system disinfection, please visit our website
www.nemco-utilities.co.uk

4. TANK CLEANING WORK
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;
For more information on tank cleaning and water system disinfection, please visit our website
www.nemco-utilities.co.uk

5. TANK CLEANING WORK
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
For more information on tank cleaning and water system disinfection, please visit our website
www.nemco-utilities.co.uk

6. TANK CLEANING WORK
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.
For more information on tank cleaning and water system disinfection, please visit our website
www.nemco-utilities.co.uk

7. TANK CLEANING WORK
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

8. NEMCO UTILITIES LIMITED
Address Email:
Nemco Utilities Ltd • info@nemco-utilities.co.uk
12 Kempson Way • sales@nemco-utilities.co.uk
Hillside Business Park • accounts@nemco-
Bury St Edmunds utilities.co.uk
Suffolk
IP32 7EA Website: http://www.nemco-
utilities.co.uk/
Telephone: 01284 724503
Fax No.: 01284 724826
For more information on tank cleaning and water system disinfection, please visit our website
www.nemco-utilities.co.uk