Current improvement programmes

Notice of Regulation: UV Biofilm


Bristol Water Plc: Purton, Cheddar, Littleton and Stowey Water Treatment works UV biofilm

Reference: BRL-2020-00004

Water undertaker as appointed under section 6 of the Water Industry Act 1991 (as amended): Bristol Water Plc, with registered number 02662226(hereinafter called ‘the Company’).

Assets affected:
T21 Purton Treatment Works
T07 Cheddar Treatment Works
T17 Littleton Treatment Works
T25 Stowey Treatment Works

  1. The Drinking Water Inspectorate (‘the Inspectorate’) has received regulation 28(1) reports of the Water Supply (Water Quality) Regulations 2016 (as amended) (‘the Regulations’) from the Company, which states that there is or has been a significant risk of supplying water from Purton, Cheddar, Littleton and Stowey Water Treatment works (and associated assets as applicable) that could constitute a potential danger to human health.
  2. Consequently, this Notice is served on the Company by the Inspectorate on behalf of the Secretary of State, under regulation 28(4) for the assets listed above, for risks associated with:



Hazard ID

Description of Risks


C001 – Total Coliforms (Confirmed)


Purton WTW UV biofilm growth


C001 – Total Coliforms (Confirmed)


Cheddar WTW UV biofilm growth


C001 – Total Coliforms (Confirmed)


Stowey WTW UV biofilm growth


C001 – Total Coliforms (Confirmed)


Littleton WTW UV biofilm growth


  1. The Company are required to satisfy the following:


(a) to maintain the following measures for the period specified in each case:

  1. Statutory sampling as defined in the aforementioned regulations (daily).
    Date: Ongoing for the duration of the notice
  2. Weekly operational sampling including parameters specified within the DWSP as defined within Annex A.
    Date: Ongoing for the duration of the notice
  3. Maintain alarms and shutdowns associated with the disinfection process and keep under review for the period of the notice.
    Date: Ongoing for the duration of the notice

(b) to review, revise or make operational the following measures, by the dates specified in each case: Littleton Treatment Works Disinfection

  1. Review and make alteration to the company disinfection policy to reflect that primary disinfection occurs using UV.
    Date: Complete
  2. Revise the wording of the company disinfection policy to reflect use of chlorine to maintain residual in downstream distribution system.
    Date: Complete
  3. Within the revised disinfection policy,document how the company addresses the risks from viruses and microbiological contaminants throughout the works.
    Date: Complete
  4. Investigate options for continual monitoring of the chlorine residual in the outlet main from Littleton WTW, prior to the first customer receiving water. The information from this monitoring can be used to validate the Ct value in vi above.
    Date: December 2021.
  5. Review the schedule of parameters currently being analysed post UV stage at Littleton works and agree with the Inspectorate any additional or any changes to be made.
    Date: Complete
  6. Revise the company site specific disinfection policy for Littleton works.
    Date: Complete

Purton, Cheddar, Littleton and Stowey Water Treatment works – UV biofouling

  1. Document the proposed pilot trial of enhanced chemical cleaning relating to the UV process and associated pipework downstream of UV reactor.
    Date: Complete
  2. Review available sample taps and ensure that samples are taken from the most appropriate location.
    Date: Complete
  3. To additionally provide a report to show findings after the first six months of this trial being in place.
    Date: Trial commencement August 2021.Report due February 2022

(c) to audit whether the measures have been effective by the following means: Littleton Treatment works disinfection

  1. Put in place a revised disinfection strategy document for Littleton works Site specific disinfection policy.
    Date: End of February 2021-Complete

Purton, Cheddar, Littleton and Stowey Water Treatment works – UV biofouling

  1. Define and keep under continuous review an audit strategy to monitor the effectiveness of the above measures.
    Date: For the duration of the Notice.
  2. The company will carry out enhanced monitoring for a range of microbiological parameters to be defined in (b)3.
    Date: Ongoing for the duration of the notice
  3. Implement the audit strategy defined in (c)1.
    Date: Ongoing

(d) not to supply water for regulation 4(1) purposes from Purton, Cheddar, Littleton and Stowey Water Treatment works, or not to so supply unless the specified conditions below are satisfied:

Not Applicable

(e) to provide the following information in the time and manner specified below to enable monitoring of progress towards the mitigation of the risks:

  1. Provide a progress report annually by 31 January and against the following milestones:
    Date: Annually by 31 January one month after date specified for each measure.
    • Step (b)3 Within the company disinfection policy the company will document how Ct is achieved and met from Littleton to the first customer in the supply system.
      Date: December 2021
    • Submit the document produced in (b)7 on the proposed pilot trial.
      Date: October 2021
    • Report on conclusions of enhanced clean in place as part of (b)9.
      Date: February 2022
    • Submit disinfection strategy reviewed in (c)1.
      Date: Complete
  2. Review the disinfection strategy for Littleton works and produce a document to show the work that was carried out pre the removal of post ozone stage and also the rationale for the disinfection process at Littleton works.
    Date: Complete
  3. Submit a report in the event that any measure of this Notice needs to be altered in any way for any reason.
    Date: Ongoing for the duration of this Notice
  4. Submit a satisfactory completion report accompanied by a revised regulation 28(1) report with Board level Director sign-off.
    Date: One year and one month after completion of works
  5. Final report.
    Date: End of November 2022

  1. Any product or substance used as a result of the requirements in this Notice must comply with regulation 31.
  2. Under regulation 28(6) the Inspectorate, on behalf of the Secretary of State, may by notice served on the Company, revoke or vary this Notice.
  3. Failure by the Company to comply with this Notice may result in enforcement proceedings under section 18 of the Water Industry Act 1991(as amended).

Laura Moss
Deputy Chief Inspector, on behalf of the Secretary of State for Environment, Food and Rural Affairs
07 December 2021
Reference: BRL-2020-00004
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