Current improvement programmes

North Mymms Works

WATER INDUSTRY ACT 1991 (as amended) : SECTION 19(1)(b)


  1. is satisfied that Affinity Water Limited “the Company” in supplying water from the North Mimms treatment works which may be at risk of exceeding the standards for metaldehyde and total pesticides. This means that the Company is likely to contravene its duty in respect of supplying water which meets the Regulations under Section 68(1)(a) of the Water Industry Act 1991 (as amended) and meets the requirement set in regulation 4(2)(c) of the Water Supply (Water Quality) Regulations 2016 (as amended).
  2. notes that Affinity Water Limited has on 20 May 2020 given a new undertaking (DWI Ref No: AFW-2020-00003) under the provisions of paragraph 2(b) of the previous undertakings given on 8 September 2016 (DWI Ref no: AFW3322) to replace the undertaking and take the following steps by the dates shown:

Steps to be taken

  • Ensure that metaldehyde has been assessed as a hazard as part of the regulation 28 Risk Assessment for the supply systems supplied by North Mymms Water Treatment Works according to a Drinking Water Safety Plan approach.

Delivery Date: Ongoing

  • The Company shall implement all actions as defined in their actions plans submitted to the Inspectorate on 30 September 2014.
    • The Company shall implement additional transitional arrangements during the period of stock use, ensuring the maintenance of supportive relationships with farming community.

Delivery Date: Ongoing as necessary until metaldehyde use is restricted in the open environment

  • Medium Term measures:
    • Continue with enhanced raw water monitoring programme to inform risk.
    • Where ongoing significant risks are identified the Company shall continue the DWSP approach and appropriate measures to mitigate the risk shall continue to be implemented.
    • Liaise with the Environment Agency where there are continued detections in raw water.

Delivery Date: Ongoing until the revocation of this undertaking.

  • Complete construction, installation and commissioning of the rapid clarification with powdered activated carbon treatment solution on the Tyttenhanger raw water stream.

Delivery Date: 30th June 2020

  • Long term measures:
    • Continually appraise the risk of metaldehyde and the total pesticides parameters as hazards in raw waters as part of the regulation 27 Risk Assessment for the supply system(s) associated with North Mymms WTW according to a Drinking Water Safety Plan approach, and ensure that Regulation 28 documents are regularly reviewed and updates provided as appropriate.

Delivery Date: Ongoing

  • Reporting: Provide DWI with reports on progress with carrying out the steps set out in the undertaking. Reports to include at least the following details:
    • Metaldehyde monitoring data for the raw and final water at North Mymms WTW including trend analysis;
    • Current state of progress with the catchment measures;
    • Current state of progress with operational controls and summary of effectiveness.

Delivery Date: Annually for the duration of the Undertaking. Reporting periods are January to December. Reports to be submitted by 31 January each year that the Undertaking is in place, (except for January 2025)

  • Provide a final report to DWI on the efficacy of the catchment solutions and the conclusions drawn from other work carried out as part of this Undertaking. Include, as evidence for closure for this scheme, appropriate documentation to confirm that the actions set out in this schedule of work have been completed and the extent to which the required outcomes have been achieved.

Delivery Date: When there is sufficient evidence of suitable mitigation of the risk (i.e. 3 years samples below 0.1ug/l and evidence of stable or decreasing raw water trends) or by 31 March 2025

  1. is satisfied that Affinity Water 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:
Milo Purcell
Deputy Chief Inspector
Drinking Water Inspectorate
DWI Ref No: AFW-2020-00003
Date: 5 June 2020