NEWS

8 Aug 2014

10 most common water storage tank remedials to achieve L8 compliance

 

Cold water storage tanks pose one of the highest risks of Legionella growth within a building’s water system, due to the possibility of stagnation, temperature gain and contamination.

Regular inspections of the tank and microbiological sampling are important features of a water hygiene control scheme required by ACoP L8, but these actions will prove inadequate if the tank design is not up to standard. To help you understand some of the current guidance notes such as BS8558, ACoP L8, HSG274 and the Water Regulations, W.E.T’s Legionella technicians have put together the top 10 most common tank repairs, which we regularly undertake to help building owners and facility managers achieve compliance, along with the relevant legislation and our recommendations from section 3.2 of our Legionella risk assessments.

1 - Cold water storage tank (CWST) has the inlet and outlets on the same side

1

Problem
Positioning the inlet and outlet closely together or on the same side does not allow good cross flow and creates pockets of stagnation where bacteria may proliferate.

Solution
Fit internal sparge pipe and log details of remedial action.

 

2 - The cold water storage tank has a damaged lid

2

Problem
A damaged lid may allow insect and vermin ingress subsequently contaminating stored water.

Solution
Replace the existing lid and log all details of all remedial action carried out.

 

3 - Access to the cold water storage tank is difficult and intrusive for monitoring

3

Problem
All cold water storage tanks should be in a cool area with adequate access for appropriate monitoring. The CWST should be inspected visually, internally and externally and cleaned and disinfected where necessary.

Solution
Improve access and implement appropriate monitoring. All remedial action must be logged.

 

4 - Cold water storage tank has a light sediment build up and debris on the base

4

Problem
Sediment and debris, including non WRAS approved materials, may provide a nutrient rich harbour for microbiological growth protecting Legionella bacteria from unfavourable temperatures, potentially leading to the CWST and its periphery becoming contaminated.

Solution
Clean and disinfect CWST removing all sediment and possible contaminants. Log all details of remedial action.

 

5 - Cold water storage tank has an open vent from the calorifier

5

This drawing shows a preferential scenario, whereby both calorifiers fitted with open vents discharge to a separate location

Problem
Calorifiers should not vent to a CWST as if the passes the stored cold water temperatures may rise into the bacterial proliferation zone.

Solution
Re-route open vent to a tundish. All details of remedial action must be logged.

 

6 - Cold water storage tank does not have a suitably screened airvent

6

Problem
All CWSTs should have an airvent to allow the CWST to breathe as the water level rises and falls. Airvents should be screened to prevent vermin/ insect ingress.

Solution
Install a screened airvent with apertures no greater than 0.65mm, log all details of remedial action.

 

7 - The cold water storage tank has a loose lid

7

Problem
An unsecure lid may allow insect and vermin ingress subsequently contaminating stored water.

Solution
Secure and fasten existing lid to tank and log details of all remedial action carried out.

 

8 - The cold water storage tank has structures creating a crevice for debris build up

8

Problem
Unsmooth finished surfaces and scale promote areas of bacterial growth. All cold water storage tanks should reach the appropriate regulation to prevent conditions that may promote bacterial proliferation of contamination of stored water.

Solution
Consideration should be given to replacing CWSTs, logging details of any remedial action.

 

9 - The cold water storage tanks are configured incorrectly allowing inadequate circulation

9

Problem
Incorrectly configured cold water storage tanks may allow the water to stagnate increasing the risks of bacterial proliferation.

Solution
Configure CWSTs in parallel to provide good flow. All remedial action must be logged.

 

10 - The warning pipe on the cold water storage tank does not discharge to a conspicuous location

10

Problem
All CWSTs over a capacity of 1001 litres must have a warning pipe discharging to a conspicuous location to give an alert that water has reached a predetermined level and may overflow.

Solution
Re-route pipe work to a location visible so that if levels rise warning is given to prevent the CWST overflowing.

 

If any of these are present within your water system, please contact the knowledgeable team at W.E.T for advice on 01827 288810.

© Water Environmental Treatment Ltd
01827 288810
enquiries@wet-services.com
Registered in England No. 2685141

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