Notice of Regulation: West Meon Treatment Works


Portsmouth Water Limited: West Meon Treatment Works, Risk to Disinfection

Reference: PRT-2020-00007 (replaces PRT4088)

Water undertaker as appointed under section 6 of the Water Industry Act 1991 (as amended): Portsmouth Water Limited, with registered number 02536455 (hereinafter called ‘the Company’).

Assets affected:

Asset Name

Asset Reference

Associated Water Supply Zones

West Meon Treatment Works


ZFDR – Firdown Supply Zone

  1. The Drinking Water Inspectorate (‘the Inspectorate’) has received a regulation 28(1) report of the Water Supply (Water Quality) Regulations 2016 (as amended) (‘the Regulations’) from the Company dated 19 January 2018, alongside subsequent reports dated 18 October 2018, which state that there is or has been a significant risk of supplying water from West Meon treatment works (and associated assets as applicable) that could constitute a potential danger to human health or could be unwholesome.
  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/Hazardous Event/Parameter

Description of Risks


  • Failure to meet requirements of regulation 26, inadequate disinfection, due to a failure to demonstrate that disinfection contact time is met under all conditions;
  • Failure to demonstrate chlorine contact time within the contact main;
  • Disinfection – Inadequate disinfection (failure to meet CT time) – microbiological and viruses and
  • Cryptosporidium

  1. The Company are required to satisfy the following:


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

Whenever water for regulation 4(1) purposes is to be supplied from West Meon treatment works ((a)1.-9.):

  1. Operate a treatment process which meets the requirements of regulation 26 in full to disinfect the water at all times and under all flow conditions.
    Date: Ongoing for the duration of this Notice
  2. Continuously review all critical control points and mitigation measures with a view to updating the Notice with additional measures where required. Ensure that any new risk identified is assessed in accordance with the Company’s Drinking Water Safety Plan (DWSP) methodology.
    Date: Ongoing for the duration of this Notice
  3. Operate all processes within defined operating ranges, with appropriate triggers, responses and contingency procedures.
    Date: Ongoing for the duration of this Notice
  4. Ensure the works control and shutdown system is operational and that monitors are calibrated at the predefined frequencies.
    Date: Ongoing for the duration of this Notice
  5. Continuous monitoring to ensure that water being presented for disinfection is of the required standard to achieve disinfection and to verify that disinfection is taking place and is effective.
    Date: Ongoing for the duration of this Notice
  6. Take action to prevent water leaving the treatment works when monitoring indicates that the water quality falls outside target range and that disinfection requirements are not met. The Company must take appropriate action to protect human health.
    Date: Ongoing for the duration of this Notice
  7. Maintain documented procedures for the escalation and investigation of any deviation from expected results or consumer complaints.
    Date: Ongoing for the duration of this Notice
  8. Take all reasonable operational steps (and continue to enhance the effectiveness) to ensure that water that is not compliant with the requirements of regulations 4 and 26 is prevented from entering supply.
    Date: Ongoing for the duration of this Notice
  9. Enhanced operational water quality monitoring to validate and verify the quality of water entering supply.
    Date: Ongoing for the duration of this Notice
  10. Implement and maintain continuous monitoring for Cryptosporidium.
    Date: Ongoing for the duration of this Notice

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

  1. Following the completion of the requirements of the Regulation 27(4) Notice PRT-2020-00002 for the Company’s catchment risk assessments for West Meon treatment works, complete a gap analysis between the reviewed and/or new risks assessment reports (as required under PRT-2020-00002) and the capabilities of the existing treatment in place.
    Date: 31 December 2021
  2. Design a disinfection and treatment process (or modify the existing process) that addresses any unmitigated risks identified through the completion of the gap analysis required under measure (b)1.
    Date: TBC (as required on the basis of the outcome of (b)1.
  3. Complete the construction, installation (or modify the existing) and commissioning of the chosen disinfection and treatment process defined by (b)2. Commissioning must include the following to account for the changes made:
    Date: TBC (as required on the basis of the outcome of (b)1.
    • Updating of the Site-Specific Disinfection Policy and any associated site-specific procedures;
    • Updating of the Site Operating Manual and removal of all out of date material from circulation; and
    • Provision of adequate training to operators on the chosen solution installed (or modified) and site operating manual under this measure.

(c) to audit whether the measures have been effective by the following means:

  1. Define an audit strategy to monitor the effectiveness of the measures specified in section (a) and (b).
    Date: 31 March 2021
  2. Implement, and keep under continuous review, the audit strategy defined in measure (c)1.
    Date: Until the revocation of this Notice

(d) not to supply water for regulation 4(1) purposes from West Meon treatment works, or not to so supply unless the specified conditions below are satisfied:

  1. Completion of measure (b)3.
    Date: Until completion of measure (b)3

(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
    • Submit a report outlining the findings of the gap analysis required under measure (b)1. and confirm the projected completion dates for measures (b)2. and (b)3.
      Date: 31 January 2022
    • Submit a report to confirm details of the strategy for auditing the effectiveness of the measures as specified in (c)1.
      Date: 30 April 2021
    • Submit a report outlining the Company’s chosen treatment design specification as defined by measure (b)1., accompanied by an updated audit strategy.
      Date: TBC
    • Submit a report documenting the completion of measure (b)3.
      Date: TBC
  2. Submit a report in the event that any completed measure of this Notice needs to be altered in any way for any reason.
    Date: Ongoing for the duration of this Notice
  3. Submit a satisfactory completion report accompanied by a revised regulation 28(1) report with Board level Director sign-off.
    Date: TBC

  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).
  4. Contravention of a regulation 28(4)(d) requirement is an offence under regulation 33(1). If guilty of such an offence, the Company is liable on summary conviction, or on conviction on indictment, to a fine. Under regulation 33(2) it is a defence for the Company to show that it took all reasonable steps and exercised all due diligence to avoid the commission of the offence.

Laura Moss
Deputy Chief Inspector, on behalf of the Secretary of State for Environment, Food and Rural Affairs
22 December 2020
Reference: PRT-2020-00007
Version 1

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