The document discusses Legionella risks associated with hot water systems. It notes that hot water cylinders are a major source of Legionella bacteria, which can spread through fine water mists. Guidelines recommend storing hot water at 60°C and distributing it at 50°C to avoid bacterial growth, but scalding regulations require lower temperatures in places like nurseries. Installing thermostatic mixer valves (TMVs) can blend hot water down to a safe temperature at outlets, but retrofitting buildings with TMVs is expensive. Some opt to store water at 40°C instead, allowing bacterial growth. TMVs also require proper installation close to outlets to prevent colonization in pipe runs.

1. - By Nemco Utilities
(www.nemco-utilities.co.uk)

2. Taking cooling tower and evaporative
condensers aside, a large proportion of
Legionella problems relating to domestic water
systems stem from hot water cylinders.
Granted, it tends to be showers that actually
create the fine mist or spray that transmit the
bacteria but the source of the bacteria seem
largely to come from stored hot water. One of
the principal reasons for this is the apparent
conflict between two separate bits of
guidance; the Legionella guidance (ACOP L8)
and the Anti-Scalding regulations.
For more information regarding TMVs or Legionella Management in general please call us on 01284 724 503
or visit our website www.nemco-utilities.co.uk

3. ACOP L8 recommends that hot water
is stored at 60 C in the cylinder and
distributed such that it reaches the
supplied outlets at a minimum of
50 C thus avoiding the temperature
at which Legionella are able to grow
effectively.
For more information regarding TMVs or Legionella Management in general please call us on 01284 724 503
or visit our website www.nemco-utilities.co.uk

4. The Anti Scalding regs state that where
vulnerable people have access to the water
services (e.g. nursery or healthcare setting)
then 50 C would be deemed at scald risk and
water should not be supplied outside the range
of 39 - 43 C. On the face of it this would
present a problem, the ideal solution is that
the water is stored at 60 C and reached the
point of use at 50 C but is blended down, by
means of a thermostatic mixer valve (TMV) or
blender tap, to a useable temperature.
For more information regarding TMVs or Legionella Management in general please call us on 01284 724 503
or visit our website www.nemco-utilities.co.uk

5. However, this is fine for new builds /
refurbishments, but to retro fit TMVs can be a
very costly and time consuming exercise with a
number of organisations preferring to turn the
hot water cylinder itself down to around 40 C.
This then provides water at a useable
temperature for washing etc but the whole hot
water system then falls within the ideal range
for bacterial growth.
For more information regarding TMVs or Legionella Management in general please call us on 01284 724 503
or visit our website www.nemco-utilities.co.uk

6. One additional problem with TMVs is that of
correct installation, having been given the
advice that these valves need fitting, it is not
uncommon for one central blending valve to be
installed in the plant room or one valve used
to serve the whole wing of a building. ACOP L8
states that TMVs should be installed ‘as close
to the point of use as possible’ essentially to
avoid long runs of pipe with water at non-
compliant temperatures, but unfortunately
does not give a definitive distance.
For more information regarding TMVs or Legionella Management in general please call us on 01284 724 503
or visit our website www.nemco-utilities.co.uk

7. TMVs are becoming more and more common,
with talk of them becoming compulsory in the
Building Regs, but there has been increasing
evidence of Legionella colonization
downstream of TMVs. This combined with
vulnerable people is not ideal.
For more information regarding TMVs or Legionella Management in general please call us on 01284 724 503
or visit our website www.nemco-utilities.co.uk

8. Nemco Utilities Ltd  info@nemco-
12 Kempson Way utilities.co.uk
Hillside Business Park  sales@nemco-
utilities.co.uk
Bury St Edmunds
 accounts@nemco-
Suffolk
utilities.co.uk
IP32 7EA
Website:
Telephone: http://www.nemco-
01284 724503 Sutilities.co.uk/
Fax No: 01284 724826
For more information regarding TMVs or Legionella Management in general please call us on 01284 724 503
or visit our website www.nemco-utilities.co.uk