South East Water Limited – Boxley Treatment Works_Disinfection Risks

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

Reference: SEW-2021-00008

Version Number: 1

Water undertaker as appointed under section 6 of the Water Industry Act 1991 (as amended): South East Water Limited, with registered number 02679874 (hereinafter called ‘the Company’).

Assets Affected:

  • R590T01 – Boxley Reservoir
  • T307T02 – Boxley Chalk Treatment Works
  • T307T03 – Boxley Greensand Treatment Work

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 21 September 2021, which states that there is or has been a significant risk of supplying water from Boxley 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

Inadequately disinfected water

Escherichia coli (E. coli)


Inadequately disinfected water

Coliform bacteria


Inadequately disinfected water



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. Optimisation of all existing treatment processes.
    Date: Ongoing for the duration of this Notice
  2. Operation of all processes within defined normal operating ranges with appropriate triggers, responses and contingency procedures.
    Date: Ongoing for the duration of this Notice
  3. Online turbidity and chlorine monitoring with appropriate alarms and failsafe shutdown.
    Date: Ongoing for the duration of this Notice
  4. Enhanced and large volume operational monitoring for microbiological parameters at Boxley Treatment Works.
    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. Install monitoring for turbidity and chlorination, to provide continuous verification of the current treatment and disinfection arrangements, on the outlet of the contact tank/reservoir.
    Date: 31 March 2022
  2. The Company shall undertake an investigation of the existing disinfection and treatment system to ensure adequate disinfection and treatment is achieved under all circumstances and flow rates and design an appropriate solution to mitigate any identified risks. The investigations must include the following:
    • The point in the treatment process whereby disinfection is achieved (the point of disinfection) must be clearly defined.
    • Investigate solution to ensure that the contact tank at Boxley Treatment Works is not used for blending with other supplies, including relocation of the Broader Lane input.
    • Investigate solution so that a designated storage reservoir is not used to achieve disinfection.
    • The final water monitoring point for Boxley Treatment Works must be located at the end of the disinfection and treatment process and be solely representative of water leaving the treatment process.
    • The disinfection system must take into account flow dynamics through the treatment works and contact tank and this must be established using appropriate techniques.
    • The disinfection system must provide safeguards such as automatic shutdown or failsafe systems to prevent untreated or partially treated water entering into supply.
      Date: 31 March 2022
  1. Clearly define the treatment and disinfection critical control points, and review, using real-time evidence, that the target chlorine contact time is achieved.
    Date: 31 July 2022
  2. Install (or modify the existing) and commission the solution as designed under measure (b)2. Commissioning must include the following to account for the changes made:
  • Full integration of the 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 to operators on the chosen solution installed (or modified) and site operating manual under this measure.
    Date: 30 April 2023

(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 August 2022
  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 Boxley 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. Provide evidence confirming completion of measure (b)1.
    Date: 30 November 2022
  3. Report the findings of the investigation completed under measure (b)2 and submit an outline of the designed solution.
    Date: 30 November 2022
  4. Confirm the defined critical control points and provide the real-time evidence used to show that the target chlorine contact time is achieved, as required under measure (b)3.
    Date: 30 November 2022
  5. Provide evidenced confirmation of completion of measures (b)4 to install and commission the designed solution and provision of training. Provide the updated Site-Specific Disinfection Policy, site procedures and Site Operating Manual.
    Date: 31 May 2023
  6. Submit the audit strategy for auditing the effectiveness of the measures, as specified in measure (c)1.
    Date: 31 December 2022
  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 May 2024

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
04 November 2022
Reference: SEW-2021-00008

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