Thames Water Utilities Limited – EN7 Goffs Oak PAH’s

Water Industry Act 1991 (as amended) (“the Act”): Section 19(1)(b)

Reference: TMS-2026-00003

Acceptance Notice:

The Drinking Water Inspectorate, on behalf of the Secretary of State for Environment, Food, and Rural Affairs:

1. Is satisfied that Thames Water Utilities Limited “the company” in supplying water from Goffs Oak Water Supply Zone has contained exceedances of the standards for polycyclic aromatic hydrocarbons (PAH’s) and is likely to do so again, has contravened its duty in respect of supplying water which meets the Regulations under Section 68(1)(a) of the Water Industry Act 1991 and the requirement set in regulation 4(2)(c) of the Water Supply (Water Quality) Regulations 2016, as amended.
2. Has notified the company on 14 April 2026 that the Secretary of State is considering making in relation to the company an enforcement order under Section 18 of the Act.
3. Notes that the company has on 12 May 2026 given a new undertaking under Section 19 (1) (b) of the Act, to take the following steps by the dates shown.

Steps to be taken:

1. Ensure that the PAH and benzo(a)pyrene parameters have been assessed as a hazard as part of the regulation 27 Risk Assessment for the supply system that includes Goffs Oak water supply zone according to a Drinking Water Safety Plan approach. Ensure that regulation 28 documents are reviewed, and updates provided as necessary.
   Date: Ongoing for the duration of the undertaking.
2. Enhanced sampling within the affected District Metered Areas (Darnicle Hill 4 and 5) to inform the ongoing risk.
   Date: Ongoing for the duration of the undertaking.
3. Regular review of water quality customer contacts within the affected District Metered Areas (Darnicle Hill 4 and 5) relating to aesthetic concern.
   Date: Ongoing for the duration of the undertaking.
4. Review the operation, and any required optimisation, of the local network. Complete the optimisation assessment for DMA ZDARNH04. The assessment is to consider historic monitoring results and updated modelling taking into consideration the planned update of the Cheshunt booster station to variable speed pumps.
   Date: 30 June 2026
5. Replacement of all the local 4” cast iron main. This includes six roads in the area surrounding the incident, as well as removal (cutting and capping) of the dead-leg section on Park Lane. Estimated length – 1,100 Metres.
   Date: 30 September 2026

Reporting:

1. Provide a summary report of the outcome of the desktop investigation and modelling as detailed under Step 4.
   Date: 31 July 2026
2. Confirm completion of replacement activities as detailed under Step 5.
   Date: 31 October 2026
3. Provide a final report to the Inspectorate on the efficacy of the steps taken as part of this undertaking. Include, as evidence of closure for this scheme, appropriate documentation to confirm that the actions set out in this Schedule of Work have been completed satisfactorily.
   Date: 31 October 2027

Further Details of this Acceptance Notice:

The Secretary of State is satisfied that Thames Water Utilities Limited has given and is complying with an undertaking to take all such steps as appear to the Secretary of State for the time being to be appropriate to secure or facilitate compliance with the requirement of regulation 4(2)(c) of the Water Supply (Water Quality) Regulations 2016 (as amended).

Authorised by the Secretary of State to sign in that behalf:

Nicholas Adjei
Deputy Chief Inspector, Drinking Water Inspectorate
14 May 2026
Reference: TMS-2026-00003