Current improvement programmes

Notice of Regulation: Netley Mill Water Treatment Works – Disinfection


Thames Water Utilities Limited: Netley Mill Water Treatment Works, Disinfection

Reference: TMS-2019-00003

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:
Netley Mill Water Treatment Works (T04U.401 – Netley Mill / Albury)
Cranleigh community (YTMS1185)

  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 13 June 2019, which states that there is or has been a significant risk of supplying water from Netley Mill 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:

Hazard/Hazardous Event/Parameter

Hazard ID

Description of Risks

  • Failure of disinfection process
  • Biological hazards (including E. coli, Total Coliforms, Enterococci, Clostridium Perfringens)


Failure of disinfection process

  1. The Company are required to satisfy the following:


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

Date: Ongoing for the duration of the Notice.

  1. Not to supply water, for regulation 4(1) purposes, that is improperly disinfected.
  2. Continuously monitor the disinfection process at Netley Mill Water Treatment Works (WTW) by means of chlorine and turbidity monitoring pre and post contact.
  3. Carry out sampling for total coliforms, E.coli, turbidity and residual disinfection at a frequency of 4 times a week.

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

  1. Deliver installation of new sampling tap and chlorine monitor at SP4 (post contact and pre dechlorination) with appropriate alarm levels to continue compliance with (a)1 and (a)2 above.
    Date: Complete (20 May 2020)
  2. To review disinfection equipment and monitors currently used on site and take appropriate actions to ensure they are fit for purpose.
    Date: Complete (31 August 2020)
  3. Based upon the review of disinfection equipment and monitors specified in step (b)2. above, replace and refurbish equipment as appropriate to ensure compliance with the Regulations.
    Date: 31 March 2022
  4. Review sampling facilities and sample loop times for current SP2 sample tap (pre-contact tank) and new SP4 tap once installed to ensure they are appropriate and in compliance with company policy.
    Date: Complete (31 August 2020)
  5. Undertake start-up and shutdown testing to confirm that new alarms are appropriate for preventing regulatory breaches.
    Date: Complete (20 May 2020)
  6. Design, install and make operational a containment system, run to waste system or other system at Netley Mill WTW to prevent improperly disinfected water from entering supply and to allow for disposal of water which is in breach of the Regulations.
    Date: 30 June 2022
  7. Update the site operating manual, site schematics, relevant procedures and Company records to account for measure (b)3. and the installation of the system designed under measure (b)6.
    Date: 30 June 2022
  8. Provide training for all relevant personnel for the new system installed under measure (b)6. and changes made under (b)3., and for any updates to documentation updated under measure (b)7.
    Date: 30 June 2022

(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 section (a) and (b).
    Date: Complete (24 July 2020)
  2. Implement, and keep under continuous review, the audit strategy defined in measure (c)1.Following completion of measure (c)1.
    Date: onwards

(d) not to supply water for regulation 4(1) purposes from Netley Mill WTW, or not to so supply unless the specified conditions 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 risks:

  1. Provide a progress report annually by 31 January and against the following milestones:
    Date: Annually by 31 January
    • Submit the audit strategy required under measure (c)1.
      Date: Complete (24 July 2020)
    • Provide a report on the suitability on the disinfection equipment and monitors used on site.
      Date: Complete (30 September 2020)
    • Confirm completion of the replacement and/or refurbishment of disinfection equipment and monitors as required under measure (b)3.
      Date: 31 April 2022
    • Evidenced confirmation that the new system (designed under measure (b)6.) is in full operation and the training and documentation review has been completed (as required under measure (b)7-8).
      Date: 31 July 2022
  2. Submit any revisions of the audit strategy produced under measure (c)2.
    Date: Within 1 month of a revision
  3. Submit a report in the event that any completed measure of this Notice needs to be altered in any way for any reason.
    Date: Ongoing for the duration of this Notice
  4. Submit a satisfactory completion report accompanied by a revised regulation 28(1) report with Board level Director sign-off.
    Date: 31 July 2023

  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).

Laura Moss
Deputy Chief Inspector, on behalf of the Secretary of State for Environment, Food and Rural Affairs
05 January 2022
Reference: TMS-2019-00003
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