Thames Water Utilities Limited – Streatham Water Treatment Works, Turbidity Risk

Notice under regulation 28(4) of the Water Supply (Water Quality) Regulations 2016 (as amended)

Reference: TMS-2022-00009

Version Number: 1

Water undertaker as appointed under section 6 of the Water Industry Act 1991 (as amended): Thames Water Utilities Limited, with registered number 02366661 (hereinafter called ‘the Company’).

Assets Affected:

Asset Name


Streatham Water Treatment Works


Hampton 42 Community Supply System


Table 1: List of assets affected and associated reference numbers

Details of this Notice:

  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 09 June 2022, which states that there is or has been a significant risk of supplying water from Streatham Water 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:

Description of Risk

Hazard/ Hazardous Event/ Parameter

Hazard I D

Turbidity. Failure to subject water to sufficient preliminary treatment to prepare it for disinfection (regulation 26(1)(b) and 26(6)(b)). Failure to verify the effectiveness of the disinfection process (regulation 26(2)(b)).



Table 2: Table of the hazards, hazardous events, and/or parameters covered by this Notice, including the Hazard I D numbers and the description of risks.
  1. The Company are required to satisfy the following requirements.

The date given is that until or by which the requirements must be maintained or satisfied, as appropriate.


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

  1. Operation of all processes within defined operating ranges with appropriate triggers, responses and contingency procedures.
    Date: Ongoing for the duration of this Notice
  2. Online turbidity monitoring of water prior to disinfection with appropriate alarms and failsafe shutdowns where applicable.
    Date: Ongoing for the duration of this Notice
  3. Ensure the water treatment works’ control and shutdown system are operational and that monitors are calibrated at predefined frequencies.
    Date: Ongoing for the duration of this Notice
  4. Continuous monitoring of raw and treated water with control systems, alarmed operating limits and automatic shutdown as appropriate.
    Date: Ongoing for the duration of this Notice
  5. Ensure that turbidity monitoring equipment is maintained in-line with manufacturers’ instructions.
    Date: Ongoing for the duration of this Notice
  6. 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 SOM is required.
    Date: Ongoing for the duration of this Notice
  7. Up-to-date and subject to continuous review, site specific disinfection policy, which identifies clearly and unequivocally how disinfection is achieved at the works.
    Date: Ongoing for the duration of this Notice
  8. Maintain contingency plans (including liaison with relevant stakeholders as appropriate) to protect human health.
    Date: Ongoing for the duration of this Notice
  9. 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

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

  1. Investigate and implement measures to ensure turbidity is less than 1 NTU prior to disinfection at Streatham Water Treatment Works.
    Date: Complete
  2. Conduct a critical review of compliance with regulation 26(1)(b) and 26(6)(b) at Streatham Water Treatment Works to ensure water leaving the treatment works has received sufficient preliminary treatment to prepare it for disinfection.
    Date: 31 March 2023
  3. Design a solution to address any risks identified through the completion of the review required under measure (b)2.
    Date: 31 May 2023
  4. Implement the chosen solution designed under measure (b)3, which must include the following to account for the changes made:
  • An appropriate maintenance regime for any installed processes;
  • Full integration of any new (or modified) processes into the site control and monitoring systems.
  • 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
  • Provisions of adequate training for all relevant personnel on the operation, repair and maintenance of any installed (or modified) process and the revised procedures, policies and manual.
    Date: 31 December 2024

(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 sections (a) and (b).
    Date: 31 March 2023
  2. Implement, and keep under continuous review, the audit strategy defined in measure (c)1.
    Date: Following completion of measure (c)1 onwards.

(d) Not to supply water for regulation 4(1) purposes from Streatham Water Treatment Works, or not to so supply unless the specified conditions below are satisfied:

  1. 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.
    Date: by 31 January each year
  2. Report the findings of the investigation completed under (b)1 and resulting measures implemented.
    Date: 28 February 2023
  3. Report the outcome of the review required under measure (b)2.
    Date: 30 April 2023
  4. Submit a report outlining the chosen solution design (measure (b)3).
    Date: 30 June 2023
  5. Confirmation of completion of measure (b)4.
    Date: 31 January 2025
  6. Submit the audit strategy for auditing the effectiveness of the measures, as specified in measure (c)1.
    Date: 30 April 2023
  7. Submit any revisions of the audit strategy produced under measure (c)2.
    Date: Within 1 month of a revision
  8. Submit a report in the event that any completed measures of this Notice need to be altered in any way, for any reason.
    Date: Ongoing for the duration of this Notice
  9. Submit a satisfactory completion report accompanied by a revised regulation 28(1) report with Board level Director sign-off.
    Date: 31 January 2026

Further Details of this Notice:

  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).


Nicholas Adjei
Deputy Chief Inspector, on behalf of the Secretary of State for Environment, Food and Rural Affairs
09 February 2023
Reference: TMS-2022-00009

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