Northumbrian Water Limited – Mosswood WTW Clarifier and Supernatant Return Improvements

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

Reference: NES-2025-00004

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. T0700335 Mosswood Water Treatment Works (Durham Supply)
2. T0021824 Mosswood Water Treatment Works (Sunderland Supply)

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 June 2025, which states that there is or has been a significant risk of supplying water from Mosswood 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:

Description of Risk	Hazard/ Hazardous Event/ Parameter	Hazard I D
Poor quality process water returned to head of works Unable to isolate clarifiers for maintenance	Cryptosporidium Oocysts	NNE_TRE_T0700335_C111_CFH NNE_TRE_ T0021824_C111_CFH
Poor quality process water returned to head of works Unable to isolate clarifiers for maintenance	Turbidity	NNE_TRE_T0700335_A002A_CFH NNE_TRE_ T0021824_A002A_CFH

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. Operation of Mosswood WTW in accordance with company policy, procedures and to internally agreed process parameters
   Date: Ongoing for the duration of this Notice
2. Proactive management of performance of clarifiers at Mosswood WTW to minimise the risk to wholesomeness.
   Date: Ongoing for the duration of this Notice
3. Ongoing monitoring of regulatory and operational sample results and online data.
   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:

Clarifier Isolation Valves

1. Review the current launder cleaning Standard Operation Procedure.
2. Date: Complete
3. Investigate the inability to isolate the clarifiers for maintenance and cleaning and identify corrective actions to prevent this occurring.
   Date: 30 June 2026
4. Complete the planning, design and procurement arrangements to enable the clarifiers to be isolated.
5. Date: 30 June 2027
6. Complete the construction, installation and commissioning of the solution to enable the clarifiers to be isolated.
7. Date: 30 June 2030

Supernatant Return Improvements

1. Identify measures to prevent wash water supernatant with turbidity greater than 10 NTU returning to the head of works.
   Date: 30 June 2026
2. Complete the planning, design and procurement arrangements for supernatant improvements.
3. Date: 30 June 2027
4. Complete the construction, installation and commissioning of the agreed solution for supernatant improvements.
   Date: 30 June 2028

(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 October 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 Mosswood WTW, 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:

Clarifier Isolation Valves

1. Provide a progress report annually.
   Date: by 31 January each year
2. Submit a report confirming the results from the review of the Standard Operating Procedure for current clarifier cleaning methods, as specified in measure (b)1.
3. Date: Complete
4. Submit a report identifying the appropriate solution to enable clarifier isolation as specified in measure (b)2.
5. Date: 31 July 2026
6. Submit a report confirming the completion of the planning, design and procurement arrangements for clarifier improvements solution, as specified in measure (b)3.
7. Date: 31 July 2027
8. Submit a report confirming the completion of the construction, installation and commissioning of the clarifier improvements solution, as specified in measure (b)4.
   Date: 31 July 2030

Supernatant Return

1. Submit a report identifying the appropriate solution to improve poor supernatant return, as specified in measure (b)5. Date: 31 July 2026
2. Submit a report confirming the completion of the planning, design and procurement arrangements for improve poor supernatant return, as specified in measure (b)6.
3. Date: 31 July 2027
4. Submit a report confirming the completion of the construction, installation and commissioning of the appropriate solution for poor supernatant return, as specified in measure (b)7.
5. Date: 31 July 2028
6. Submit the audit strategy for auditing the effectiveness of the measures, as specified in measure (c)1.
   Date: 30 November 2025
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.
10. Date: 31 July 2031

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
18 August 2025
Reference: NES-2025-00004