Current improvement programmes

Notice of Regulation: Chellow Heights – AMP7 Disinfection By-products


Yorkshire Water Services Limited: Chellow Heights AMP7 Disinfection By-products

Reference: YKS-2018-00005

Water undertaker as appointed under section 6 of the Water Industry Act 1991 (as amended): Yorkshire Water Services Limited, with registered number 02366682(hereinafter called ‘the Company’).

Assets affected:

  • Chellow Heights WTW
  • Chellow Water Supply System (YSA100130844)
  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 20 September 2018, which states that there is or has been a significant risk of supplying water from Chellow Heights water treatment works (and associated assets as applicable) that could constitute a potential danger to human health.
  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:
  • Disinfection by-products
  • Trihalomethanes
  • Halo acetic acids


(a) to maintain the following measure[s] for the period specified [in each case]

Date: Ongoing for the duration of this Notice

  1. Continue to regularly monitor raw water trends for the parameter colour and keep under review dissolved organic carbon trends from on-line monitoring (UV254).
  2. Optimise existing processes to minimise the risk of DBP formation.
  3. Regularly monitor treated, stored, and distributed water for disinfection by-products(trihalomethanes and halo acetic acids).
  4. Continue to review opportunities for catchment management activities with stakeholders to implement protective measures and reduce the risk of deterioration of raw water quality, and implement those measures agreed with the EA as part of the AMP7 WINEP.

(b) to review, revise and/or make operational the following measures, by the date specified below:

  1. Regularly monitor treated water, water within key service reservoirs, and distributed water for DBPs (THMs and HAAs).
    Date: For the duration of this notice
  2. Regularly review the level of residual DOC remaining from raw water following the existing processes and ensure its removal is optimised (including the optimisation of coagulation pH and coagulant dose, and the minimisation of RGF turbidity) Regulatory review WTW performance within Water Quality and Production Operational teams to maintain optimised conditions.
    Date: For the duration of this notice
  3. Confirm the chosen solution and provide outline design for additional removal of DOC from the Nidd Aqueduct inlet, following engineering and process reviews and, where required, pilot trials
    Date: Complete
  4. Provide a detailed design of the proposed solution
    Date: 31 March 2022
  5. Install, commission, and verify through testing, the chosen solution
    Date: 31 March 2024

(c) to audit whether the measures have been effective by the following means:

  1. Define a strategy for auditing the effectiveness of the above measures. To include:
    Date: Complete
    • Sampling and data analysis for DBPs (THMs & HAAs) with a focus on ex-works and distributed water
    • Development of an auditable means by which the Company will demonstrate minimisation of DBP risks at the upgraded works under all raw water conditions
  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 Chellow Heights unless the conditions specified below are satisfied

  1. That all reasonable operational steps have been taken to ensure that water that is not compliant with the requirements of regulations 4 and 26, or that is potentially harmful to consumers, is prevented from entering supply.
    Date: Ongoing for the duration of this notice

(e) to provide the following information in the time and manner specified below to enable monitoring of progress towards the mitigation of the risk of supplying water that would constitute a potential danger to human health:

  1. Provide a progress report annually by 31 January, including details of on-going mitigations, and against the following milestones:
    • Completion of investigations, pilot trials and development of outline design
      Date: Complete
    • Completion of detailed design of the proposed solution
      Date: 30 April 2022
    • Completion of Installation and commissioning, of the chosen solution
      Date: 30 April 2024
  2. Submit any revisions of the audit strategy produced under measure (c)2.
    Date: Within 1 month of a revision
  3. Submit a report in the event that any completed measure of this Notice needs to be altered in any way for any reason.
    Date: Ongoing for the duration of this Notice
  4. Submit a satisfactory completion report accompanied by a revised regulation 28(1) report with Board level Director sign-off.
    Date: 30 April 2025

  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).
  4. Contravention of a regulation 28(4)(d) requirement is an offence under regulation 33(1). If guilty of such an offence, the Company is liable on summary conviction, or on conviction on indictment, to a fine. Under regulation 33(2) it is a defence for the Company to show that it took all reasonable steps and exercised all due diligence to avoid the commission of the offence.

Laura Moss
Deputy Chief Inspector, on behalf of the Secretary of State for Environment, Food and Rural Affairs
8 July 2021
Reference: YKS-2018-00005
Version Number: 2