Thames Water Utilities Limited – Clatford Water Treatment Works, Bentazone Risk

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

Reference: TMS-2021-00005

Version Number: 3

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:

  • Clatford Water Treatment Works (T07U.713)
  • Clatford Catchment (C07U.713)
  • Clatford water supply zone (Z0213)
  • Marlborough Community Supply System (YTMS1208)

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 22 January 2021, which states that there is or has been a significant risk of supplying water from Clatford 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

Detection of the pesticide bentazone in the raw water above the drinking water standard.




Table 1: 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. Enhanced operational monitoring for bentazone in the raw and treated water. Report any operational bentazone exceedances in the treated water to the Inspectorate as soon as practicable.
    Date: Ongoing for the duration of this Notice
  2. Liaison with relevant health authorities as appropriate to inform the assessment of risk to human health.
    Date: Ongoing for the duration of this Notice
  3. Ongoing investigations into potential sources of bentazone in the catchment. Including, targeted catchment liaison initiatives with relevant stakeholders.
    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:

Initial scoping

  1. Complete initial feasibility scoping so as to confirm the preferred solution for progression to design.
    Date: Complete (28 February 2022)

Network solution

  1. Review the network options available that would allow for the introduction of an alternative supply of water into the Clatford water supply zone, which would manage the risk from bentazone. Confirm which of these options is the Company’s chosen network solution.
    Date: 31 March 2023
  2. Develop the outline design of the chosen network solution from measure (b)2. Using the information from the outline design, review the feasibility of the chosen solution against the ongoing network schemes that it may be dependent upon. Determine whether the chosen network solution is viable or whether the treatment solution (designed under measure (b)5) needs to be progressed.
    Date: 31 January 2024
  3. Provided the outcome of measure (b)4 identifies the chosen network solution as viable, produce a detailed design of the chosen network solution.
    Date: 31 January 2025

Treatment solution

  1. Produce the design of the chosen treatment solution to mitigate the risk from bentazone.
    Date: 30 June 2023

Final solution

  1. Following the completion of measures (b)4 and (b)5, determine the final solution.
    Date: 01 February 2025
  2. Deliver the final solution determined under measure (b)6.
    Date: 30 September 2027

(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: Complete
  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 Clatford 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. Outline the feasibility scoping outcome and the preferred option being progressed to design, as required under measure (b)1.
    Date: Complete (24 March 2022)
  3. Summarise the findings of the review completed under measure (b)2 and confirm the chosen network solution.
    Date: 30 April 2023
  4. Provide the outline design of the chosen network solution and confirm its feasibility (measure (b)3).
    Date: 29 February 2024
  5. Provide the detailed design of the chosen network solution (measure (b)4). Confirm the final solution (measure (b)6).
    Date: 28 February 2025
  6. Provide the detailed design of the chosen treatment solution (measure (b)5).
    Date: 31 July 2023
  7. Confirm completion of final solution (measure (b)7).
    Date: 31 October 2027
  8. Submit the audit strategy for auditing the effectiveness of the measures, as specified in measure (c)1.
    Date: Complete (16 February 2022)
  9. Submit any revisions of the audit strategy produced under measure (c)2.
    Date: Within 1 month of a revision
  10. 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
  11. Submit a satisfactory completion report accompanied by a revised regulation 28(1) report with Board level Director sign-off.
    Date: 31 October 2028

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
13 March 2023
Reference: TMS-2021-00005 v3

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