Current improvement programmes

Notice of Regulation: Thames Water – Turbidity, All Sites




Legal Instrument Database Reference number: TMS3912

Site Names and references: see Annex 1


  1. has on 21 October 2017 and subsequent updates in January and February 2018 received a set of regulation 28 reports (the “Reports”) from Thames Water Utilities Ltd (the “Company”) which states that there is or has been a significant risk of supplying water from all sites (as listed in Annex 1, Table A)that could constitute a potential danger to human health and could be unwholesome.
  2. GIVES NOTICE to the Company under regulation 28(4) of the Water Supply (Water Quality) Regulations 2016 (as amended) that it must satisfy the following requirements:

For risks associated with:

  • Turbidity and disinfection


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

Date: Ongoing for the duration of the Notice (for all sites)

  1. Operation of all processes within defined operating ranges with appropriate triggers, responses and contingency procedures with associated review programmes.
  2. Online turbidity monitoring of water prior to disinfection with appropriate alarms and failsafe shutdowns where applicable.
  3. Ensure the works’ control and shutdown system is operational and that monitors are calibrated at predefined frequencies.
  4. Continuous monitoring of raw and treated water with control systems, alarmed operating limits and automatic shutdown as appropriate.
  5. Ensure that turbidity monitoring equipment is maintained in-line with manufacturers’ instructions.
  6. Water quality response procedures for: investigation of contraventions including process optimisation and reporting; customer complaints procedures; event response procedures for event actions and notification criteria.
  7. Up-to-date Site Operating Manual (SOM), defining normal operating ranges, triggers, response and contingency procedures, with controlled update and review programmes. Internal waiver process is followed where deviation from the SOM is required.
  8. Up-to-date and subject to continuous review, site specific disinfection policy, which identifies clearly and unequivocally how disinfection is achieved at the works.
  9. Maintain contingency plans to protect human health in the event of a risk to human health associated with drinking water quality, which should include liaison with local authorities and Public Health England to agree any actions needed to protect human health and issuing of advice to consumers, where required.
  10. In accordance with the requirements of regulation 27(3), continuously review and revise as necessary the regulation 27 risk assessment for the sites and submit revised regulation 28 reports to the Inspectorate as necessary, in accordance with the published procedure.
  11. Take all reasonable operational steps (and continue to enhance the effectiveness of these) to ensure that water that is not compliant with the requirements of regulations 4 and 26 is prevented from entering supply.

(b) to review, revise and/or make operational the following measures, by the date specified below:

Measures for all sites (Annex 1, Table A):

  1. Complete a critical review and revision of the Company’s current turbidity management policy and its ability to comply with the Regulations. This review must include:
    Date: 31 May 2019
    • The appropriateness of turbidity alarms and shutdowns to ensure compliance with the Regulations; and
    • How representativeness of turbidity monitors will be achieved and maintained.
    • a) Complete a gap analysis to identify the sites that do not comply with the Company’s revised turbidity management policy completed under measure (b)1.
      Date: 31 August 2019
    • b) Identify measures to address the findings of the gap analysis completed in measure (b)2.a) above.
      Date: 30 November 2019
    • c) Implement the measures identified under (b)2.b) above.
      Date: 29 March 2024
  2. Ensure that any water that is not compliant with the requirements of regulations 4 and 26 is unable to enter supply.
    Date: 30 April 2022
  3. Ensure regular verification of the on-line turbidity monitoring equipment in-line with good practice. Verification shall be carried out at a minimum frequency of once every calendar week.
    Date: 01 April 2019

Measures for groundwater sites:

  1. Install post disinfection turbidity monitors at Table B sites that are used for regulation 4(1) purposes.
    Date: 30 April 2022
    • a) Carry out a review of all groundwater sites (Table C sites) to determine compliance with regulation 26. This must include:
      Date: 30 August 2020
      • Representativeness of on-line turbidity measurements of the water that is presented for disinfection
      • Complete a site survey to understand travel times and ensure water being analysed is representative
    • b) Implement measures to address any deficiencies identified through (b)6.a) above. This must include:
      Date: 31 December 2020
      • The installation and commissioning of such equipment to prevent the measurement of turbidity being unrepresentative of the water leaving the water treatment works at any sites where this is found to be the case.

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

  1. Define a strategy for auditing the effectiveness of the above measures and to ensure a programme of ongoing proactive risk assessment is enacted incorporating any lesson learnt from the completion of said measures.
    Date: 2 months after serving of this Notice
  2. Implement the audit strategy outlined in section (c).
    Date: Until revocation of this Notice

(d) not to supply water for regulation 4(1) purposes from the sites in Annex A, Table A unless the conditions specified below are satisfied:

  1. n/a

(e) to provide the following information in the time and manner specified below to enable monitoring of progress towards the mitigation of the risk of supplying water that would constitute a potential danger to human health:

  1. Provide a progress report annually by 31 January and against the following milestones:
    • a) Report to confirm details of the strategy for auditing the effectiveness of the measures as specified in section (c).
      Date: 3 months after serving of this Notice
    • b) Report outlining the findings of the review completed under measure (b)1.
      Date: 30 June 2019
    • c) Report outlining the findings of the gap analysis completed under measure (b)2.a) and the measures to be taken to address any deficiencies identified (as confirmed through measure (b)2.b)) and their proposed timescales for delivery.
      Date: 31 December 2019
    • d) Confirmation of the completion of measure (b)2.c).
      Date: 01 June 2024
    • e) Confirmation of the completion date for measure (b)3.
      Date: 31 December 2019
    • f) Confirmation of completion of measure (b)3.
      Date: 01 July 2022
    • g) Confirmation of completion of measure (b)4.
      Date: 30 April 2019
    • h) Report outlining the action plan (including dates) for the installation of post disinfection turbidity monitors, on a risk prioritisation basis, that is required under measure (b)5.
      Date: 30 November 2018
    • i) Confirmation of completion of measure (b)5.
      Date: 01 July 2022
    • j) Report confirming the outcome of the review completed under (b)6.a) and any measures required to address any identified deficiencies (including timescales thereof).
      Date: 30 September 2020
    • k) Confirmation of completion of measure (b)6.b).
      Date: 28 February 2021
  2. Review the risk assessment for the water treatment works covered by this Notice as required by regulation 27(3) and subsequently submit a revised regulation 28 report accompanied by a signed board level declaration.
    Date: Two months after the completion of all measures in section(b)
  3. Submit a satisfactory completion report.
    Date: 06 May 2025

Failure by the Company to comply with this Notice may result in enforcement proceedings under section 18 of the Act.

Signed by authority of the Secretary of State
Laura Moss
Deputy Chief Inspector
08 July 2020
DWI ref: TMS391
Version 2