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

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

Reference: TMS-2019-00003

Version Number: 5

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


Netley Mill/ Albury


Cranleigh Community


Table 1: List of assets affected and associated reference numbers

Details of this Notice:

  1. The Drinking Water Inspectorate (‘the Inspectorate’) has received a set of regulation 28(1) report of the Water Supply (Water Quality) Regulations 2016 (as amended) (‘the Regulations’) from the Company on 13 June 2019, which state that there is or has been a significant risk of supplying water from Netley Mill 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

Potential risks from storage of water in tanks; including contamination from ingress or egress, and microbiological re-growth.

Contamination / Physio Chemical/ Biological

For example: TMS-4-T04U.401-HEID051-T04U.401-H062

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. Not to supply water, for regulation 4(1) purposes, that is improperly disinfected.
    Date: Ongoing for the duration of this Notice.
  2. Continuously monitor the disinfection process at Netley Mill Water Treatment Works (WTW) by means of chlorine and turbidity monitoring pre and post contact.
    Date: Ongoing for the duration of this Notice
  3. Carry out sampling for total coliforms, E. coli, turbidity and residual disinfection at a frequency of 4 times a week.
    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. 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
  2. To review disinfection equipment and monitors currently used on site and take appropriate actions to ensure they are fit for purpose.
    Date: Complete
  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: Complete
  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
  5. Undertake start-up and shutdown testing to confirm that new alarms are appropriate for preventing regulatory breaches.
    Date: Complete
  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: 31 March 2025
  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: 31 March 2025
  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: 31 March 2025

(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 Netley Mill/ Albury, 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 a report on the suitability on the disinfection equipment and monitors used on site.
    Date: Complete
  3. Confirm completion of the replacement and/or refurbishment of disinfection equipment and monitors as required under measure (b)3.
    Date: Complete
  4. 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 measures (b)7-8.
    Date: 30 April 2025
  5. Submit the audit strategy for auditing the effectiveness of the measures, as specified in measure (c)1.
    Date: Complete
  6. Submit any revisions of the audit strategy produced under measure (c)2.
    Date: Within 1 month of a revision
  7. 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.
  8. Submit a satisfactory completion report accompanied by a revised regulation 28(1) report with Board level Director sign-off.
    Date: 30 April 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
8 August 2023
Reference: TMS-2019-00003 V5

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