Current improvement programmes

Notice of Regulation: Watlington Water Treatment Works



THAMES WATER UTILITIES LTD: Watlington Cryptosporidium

Watlington water treatment works T05U.509

Legal Instrument Database Reference number: TMS3960


  1. has received a report from Thames Water Utilities Ltd (the “Company”) dated 29 January 2018 (the “Report”) which states that there is or has been a significant risk of supplying water from Watlington water treatment works that could constitute a potential danger to human health and could be unwholesome.
  2. GIVES NOTICE to the Company under regulation 28(4) of the Water Supply (Water Quality) Regulations 2016 (as amended) that it must satisfy the following requirements:

For risks associated with:

  • Cryptosporidium and inadequate treatment for the risks posed by the characteristics of the raw water.
  • Presence of Cryptosporidium in final water
  • Contamination from sources of Cryptosporidium


(a) to maintain the following measures for the period specified:

To ensure that wholesome water is supplied to consumers at all times, in accordance with the requirements of regulation 4, maintain existing operational measures which must include the following:
Date: With immediate effect and ongoing for the duration of the Notice.

  1. Continuous sampling for Cryptosporidium oocysts.
  2. Operation of all processes within defined operating ranges with appropriate triggers, responses and contingency procedures.
  3. Online turbidity monitoring pre-contact tank with appropriate alarms and failsafe shutdown where applicable.
  4. Ensure the works control and shutdown system is operational and that monitors are calibrated at the predefined frequencies.
  5. Enhanced operational monitoring for microbiological faecal indicators.
  6. Continuously review all critical control points and mitigation measures for the duration of this Notice with a view to updating the Notice with additional measures where required. Ensure that any new risk identified is assessed in accordance with the Company’s Drinking Water Safety Plan (DWSP) methodology.
  7. Water quality response procedures for: investigation of contraventions including process optimisation and reporting; customer complaints procedures; event response procedures for event actions and notification criteria.
  8. Up to date Site Operating Manual (SOM), defining normal operating ranges, triggers, response and contingency procedures, with controlled update and review programmes. Internal waiver process is followed where deviation from SOM is required.
  9. Maintain contingency plans to protect human health in the event of a risk to human health associated with drinking water quality, which should include liaison with local authorities and Public Health England to agree any actions needed to protect human health and issuing of advice to consumers, where required.

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

  1. Complete the planning, design and procurement of an effective treatment process for the removal or inactivation of Cryptosporidium to comply with the Badenoch and Bouchier recommendations1 and to secure the long term protection of human health of those consumers receiving water from the associated supply system(s). This must include consideration of maximum design capacities, operational envelopes and redundancies of the chosen long term solution.
    Date: 30 September 2020
  2. Complete the construction, installation and commissioning of the chosen solution identified in (b)1. above.
    Date: 31 March 2021

1 Cryptosporidium in Water Supplies, Reports of the Groups of Experts published in 1990, 1995 and 1998.

(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.
    Date: 2 months after Notice served date
  2. Implement the audit strategy outlined above.
    Date: Until revocation of this Notice.

(d) not to supply water for regulation 4(1) purposes from Watlington water treatment works unless the conditions specified below are satisfied:

  1. n/a

(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 and against the following milestones:
    • Report to confirm details of the strategy for auditing the effectiveness of the measures as specified in section (c).
      Date: 3 months after Notice served date
    • Confirmation of the chosen long term solution confirmed under measure (b)1.
      Date: 31 October 2020
    • Confirmation of the installation and commissioning of the long term solution completed under measure (b)2.
      Date: 30 April 2021
  2. Review the risk assessment for Watlington water treatment works as required by regulation 27(3) following the completion of all measures in section (b) and subsequently submit a revised regulation 28 report accompanied by a signed board level declaration.
    Date: 21 May 2021
  3. Submit a satisfactory completion report.
    Date: 30 April 2022

Failure by the Company to comply with this Notice may result in enforcement proceedings under section 18 of the Act.

Signed by authority of the Secretary of State
Laura Moss
Deputy Chief Inspector
28 September 2018
DWI ref: TMS3960
Version 1