Northumbrian Water Limited – Company-wide Disinfection

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

Reference: NES-2025-00003

Version Number: 1

Water undertaker as appointed under section 6 of the Water Industry Act 1991 (as amended): Northumbrian Water Limited, with registered number 02366703 (hereinafter called ‘the company’).

Assets Affected:

1. All company works where disinfection occurs or is completed within the works boundary.

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 11 September 2024, which states that there is or has been a significant risk of supplying water from all company 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	Example Hazard ID (all examples from Horsley WTW unique IDs)
Cryptosporidium in the final water and associated supply zone.	Cryptosporidium	NNE_TRE_T0700330_C111_CFH, Carried forward hazard
Coliform bacteria in the final water and associated supply zone.	Coliform bacteria	NNE_TRE_T0700330_C001_CFH,  Carried Forward Hazard
Enterococci in the final water and associated supply zone.	Enterococci	NNE_TRE_T0700330_C003_CFH, Carried Forward Hazard
Escherichia coli in the final water and associated supply zone.	Escherichia coli	NNE_TRE_T0700330_C002_CFH, Carried Forward Hazard

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.

3. 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. Continuous online monitoring of UV system performance validation parameters with appropriate alarms and failsafe shutdowns to ensure compliance with the site disinfection policies (method statements) where applicable. 
   Date: Ongoing for the duration of this Notice
2. Continuous online monitoring of flow and level in disinfection stage/process sections. Where t10 is measured, verify this using an appropriate flow measurement and level detection. Ensure appropriate alarms and failsafe shutdowns are in place for sites where this monitoring is active. These monitors should be used to continuously verify the Ct10 calculated value. 
   Date: Ongoing for the duration of this Notice
3. Monitor Cryptosporidium based on the risk informed company strategy.
   Date: Ongoing for the duration of this Notice
4. Ensure that turbidity, pH, free chlorine, flow, level and ultra-violet (UV) system performance validation equipment is maintained in-line with manufacturers’ instructions.
   Date: Ongoing for the duration of this Notice
5. Operate all processes within defined operating ranges with appropriate triggers, responses and contingency procedures. 
   Date: Ongoing for the duration of this Notice
6. Update and continuously review, site specific disinfection policies (method statements), which identify clearly and unequivocally how disinfection is achieved at each water treatment works. 
   Date: Ongoing for the duration of this Notice
7. Maintain contingency plans (including liaison with relevant stakeholders as appropriate) to protect human health. 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. Implement additional training around the disinfection policy and develop a policy around third-party liaison and handover. Date: 31 May 2026
2. Develop a comprehensive report that outlines the rationale behind the company’s use of a static data mixed-source approach to applying varying health-based targets instead of adopting a uniform 1 x 10^-6 DALY per person per year on all its treatment sites. The report should include a review of the references utilised to support the static data as part of the DALY calculation. Additionally, include the approach the company plan to take in achieving the 1 x 10^-6 DALY target, providing evidence of the rational for the updated frequencies for the data sources used, including the static data used for the DALY calculation.
   Date: 31 December 2025
3. Compile a report detailing how the company defines its raw water data sets and how it categorises the multiple raw water sources supplying a single water treatment works. Date: 30 September 2025
4. Gather and document the sample types that are included in the company’s raw water classification calculation, detailing how many samples are to be taken out of hours or during poor weather events. Update the disinfection policy to explain how percentiles of data are used and clearly outline how the policy is followed. Date: 30 September 2025
5. Update the company disinfection policy to include information explaining the sanitary survey and how this is incorporated into the raw water classification. Date: 30 September 2025
6. Update the company’s disinfection policy to clearly define how turbidity is being monitored and outline the procedures to follow when turbidity limits for log credits are breached. Date: 30 September 2025
7. Within the company’s disinfection policy, define marginal chlorination and the requirements for this, including a definition of failure of marginal chlorination. Date: 30 September 2025
8. Within the company’s disinfection policy, include the details for references and sources of information for chlorine inactivation. Date: 30 September 2025
9. Review and update the company’s disinfection policy and data extrapolation procedures to ensure detailed justification is provided when more than 4 log₁₀ removal or inactivation is claimed for any process. Date: 30 September 2025
10. Review and update or confirm all current SCADA calculations for effective Ct (eCt) match those provided in the company’s disinfection policy and define how the minimum eCt is calculated and how it relates to Water Quality targets and disinfection requirements. Date: 31 May 2026
11. Specify, in the company’s disinfection policy, the maximum pH permitted for disinfection calculations and include supporting evidence for disinfection efficacy (inactivation) is provided within the policy, up to this pH. Date: 30 September 2025
12. Define and detail the log removal credits in the company’s disinfection policy. Date: 30 September 2025
13. Update the company’s disinfection policy to include the company standard for determining t₁₀ and baffle factors Date: 30 September 2025
14. Update the company’s disinfection policy to include details of the methodology used for the adjustment factors and the reasoning for using 48,000J/mol. Date: 30 September 2025
15. Ensure the approach to UV treatment in the disinfection policy aligns with the company’s site-specific UV treatment policies. Date: 30 September2025
16. Compile a report outlining the company’s process for document control of the disinfection policy, including site specific disinfection policies, defined roles and responsibilities, training requirements, sign off protocols and auditing mechanisms. Date: 30 September 2025
17. Clarify and document regulation 26 requirements, including definitions of disinfection failures and the necessary conditions needed in relation to log removal and Ct compliance. Date: 30 September 2025
18. Implement a company procedure to ensure that paper-based monitor validation sheets are regularly reviewed to ensure the required information is recorded accurately and errors can be identified and corrected. Date: 31 December 2025
19. Include within an appropriate policy for online monitors, the permitted tolerance for all monitor types and the references from which these values were derived. Date: 30 September 2025
20. Include suitable reference material in the policy for online monitors to ensure understanding of calibration and validation solutions, such as StablCal. Date: 30 September 2025
21. Define, in the policy for online monitors, the calibration frequency requirements for each type of online monitor and outline how these frequencies are validated through on-site checks. Date: 30 September 2025
22. Include full loop calibration (electrical) and dark testing as part of the calibration protocol at a suitably evidenced frequency. Date: 31 December 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: 31 July 2025
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 all company 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. Submit evidence of the additional training implemented around the disinfection policy, including the policy around third-party liaison and handover, as specified in measure (b)1. Date: 30 June 2026
2. Submit the report explaining the reasons behind the company’s static data mixed-source approach to utilising varying health-based targets instead of choosing 1 x 10^-6 DALY per person per year on all its treatment sites, including a review of the references utilised for the static data as part of the DALY calculation. Also include the approach the company will take to reach the 1 x 10^-6 DALY level, with evidence of the rational on the updated frequencies for the data sources used, including the static data for the DALY calculation, as specified in measure (b)2.
   Date: 31 January 2026
3. Submit the report detailing how the company defines its raw water data sets and how it categorises the multiple raw water sources supplying a single water treatment works, as specified in measure (b)3. Date: 31 October 2025
4. Submit in a report the details regarding which sample types are included in the company’s raw water classification calculation, including how many samples are to be taken out of hours or during poor weather events. Provide details within the disinfection policy of how percentiles of data are used and specify how the policy is followed, as specified in measure (b)4.
   Date: 31 October 2025
5. Submit evidence of the updated company disinfection policy showing the inclusion of information explaining the sanitary survey and how this is incorporated into the raw water classification, as specified in measure (b)5. Date: 31 October 2025
6. Submit evidence of the updates made to the company’s disinfection policy stating clearly how turbidity is being monitored and the procedures applied when turbidity limits for log credits are breached, as specified in measure (b)6.
   Date: 31 October 2025
7. Submit evidence of the updates made to the company’s disinfection policy stating clearly how marginal chlorination has been defined and the requirements for this, including a definition of failure of marginal chlorination, as specified in measure (b)7. Date: 31 October 2025
8. Submit the evidence showing references and sources of information for chlorine inactivation have been included within the company’s disinfection policy, as specified in measure (b)8. Date: 31 October 2025
9. Submit the evidence confirming the company’s disinfection policy data extrapolation procedures have been updated to ensure details are provided when more than 4 log₁₀ removal or inactivation is claimed for any process, as specified in measure (b)9. Date: 31 October 2025
10. Submit the evidence confirming all current SCADA calculations have been updated for effective Ct (eCt) to match those provided in the company’s disinfection policy. Also include within the policy the company’s definition of how the minimum eCt is calculated and how it relates to WQ targets and disinfection requirements, as specified in measure (b)10. Date: 30 June 2026
11. Submit evidence that the company’s disinfection policy now includes the maximum pH permitted for disinfection calculations and that referenced evidence for disinfection (inactivation) is provided within the policy up to this pH, as specified in measure (b)11.
    Date: 31 October 2025
12. Submit an audit strategy to monitor the effectiveness of the measures specified in sections (a) and (b), as specified in measure (c)1. Date: 31 August 2025
13. Submit any revisions of the audit strategy produced under measure (c)2.
    Date: Within 1 month of a revision
14. Submit evidence which shows log removal credits have been defined and detailed within the company’s disinfection policy, as specified in measure (b)12. Date: 31 October 2025
15. Submit evidence to show the company’s disinfection policy has been updated to include the company standard for determining t₁₀ and baffle factors, as specified in measure (b)13. Date: 31 October 2025
16. Submit evidence to show the company’s disinfection policy includes details of the methodology used for the adjustment factors and the reasoning for using 48,000J/mol, as specified in measure (b)14. Date: 31 October 2025
17. Submit evidence demonstrating the approach to UV treatment in the disinfection policy aligns with the company’s site-specific UV treatment policies, as specified in measure (b)15. Date: 31 October 2025
18. Submit a report explaining the company’s process for document control of the disinfection policy, site specific disinfection policies, roles and responsiblities, training, sign off and auditing of the process, as specified in measure (b)16. Date: 31 October 2025
19. Submit evidence that regulation 26 and disinfection failures and requirements needed in relation to log removal and Cthave been defined within the company’s disinfection policy, as specified in measure (b)17. Date: 31 October 2025
20. Submit the company procedure that ensures staff regularly check paper-based monitor validation sheets for errors, as specified in measure (b)18. Date: 31 October 2025
21. Submit evidence of the inclusion within an appropriate policy for online monitors, the permitted tolerance for all monitor types and the references from which these values were derived, as specified in measure (b)19. Date: 31 January 2026
22. Submit evidence to show suitable reference material has been included in the policy for online monitors to ensure understanding of calibration and validation solutions, such as StablCal, as specified in measure (b)20. Date: 31 October 2025
23. Submit evidence to show the policy for online monitors includes the calibration frequency requirement for each type of online monitor and how these frequencies are validated through on-site checks, as specified in measure (b)21. Date: 31 October 2025
24. Submit evidence to show that Include full loop calibration (electrical) and dark testing, as part of the calibration protocol, are evidenced at a suitably frequency, as specified in measure (b)22. Date: 31 January 2026
25. 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
26. Submit a satisfactory completion report accompanied by a revised regulation 28(1) report with Board level Director sign-off.
    Date: 31 July 2026

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
12 May 2025
Reference: NES-2025-00003