Thames Water Utilities Limited – Hawridge Turbidity Risks

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

Reference: TMS-2026-00004

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:

• Hawridge Works T05U.505

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 15 Jan 2026, which states that there is or has been a significant risk of supplying water from Hawridge 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
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)); and Turbidity.	A002A – Turbidity Indicator	TMS-4-T05U.505-MDCT168-T05U.505-A002A

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.

Requirements:

(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 with associated review programmes.
   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. 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.
   Date: Ongoing for the duration of this Notice
7. Up-to-date Site Operating Manual (SOM), defining normal operating ranges, triggers, response and contingency procedures, with controlled update and review programmes.
   Date: Ongoing for the duration of this Notice
8. The Company’s internal waiver process is followed where deviation from the Asset Standard is required. This must not affect compliance with the Regulations.
   Date: Ongoing for the duration of this Notice
9. 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
10. Maintain contingency plans (including liaison with relevant stakeholders as appropriate) to protect human health.
    Date: Ongoing for the duration of this Notice
11. Take all reasonable operational steps (and continue to enhance the effectiveness of those steps) to ensure 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. Conduct a critical review of compliance with regulation 26(1)(b) and 26(6)(b) at Hawridge Water Treatment Works to ensure water leaving the treatment works has received sufficient preliminary treatment to prepare it for disinfection. Subject to the critical review:
   • Submit a change application to design a solution to address any risks identified, or;
   • Provide a report detailing the implementation of measures to ensure turbidity is less than 1 NTU prior to disinfection.
     Date: 31 January 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: 30 June 2026
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 Hawridge 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. Provide the findings of the critical review regarding compliance with regulation 26(1)(b) and 26(6)(b) at Hawridge works to ensure water leaving the treatment works has received sufficient preliminary treatment to prepare it for disinfection. Provide either:
   • Confirmation of the submission of a change application to include the design of a solution to address any risks identified, or;
   • Provide a report detailing the implementation of measures to ensure turbidity is less than 1 NTU prior to disinfection.
     Date: Date: 28 February 2027

3. Submit the audit strategy for auditing the effectiveness of the measures, as specified in measure (c)1.
   Date: 31 July 2026
4. Submit any revisions of the audit strategy produced under measure (c)2.
   Date: Within 1 month of a revision
5. 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
6. Submit a satisfactory completion report accompanied by a revised regulation 28(1) report with Board level Director sign-off.
   Date: 29 February 2028

Further Details of this Notice:

4. Any product or substance used as a result of the requirements in this Notice must comply with regulation 31.
5. 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.
6. 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).

Signed

Nicholas Adjei
Deputy Chief Inspector, on behalf of the Secretary of State for Environment, Food and Rural Affairs
14 April 2026
Reference: TMS-2026-00004