Thames Water Utilities Limited – Multiple Sites Verification of Disinfection

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

Reference: TMS-2025-00003

Version Number: 1

Water undertaker as appointed under section 6 of the Water Industry Act 1991 (as amended): Thames Water Utilities Limited, with registered number 02366661 (hereinafter called ‘the company’).

Assets Affected:

• Multiple works listed in Annex 1.

Details of this Notice:

1. The Drinking Water Inspectorate (‘the Inspectorate’) has received various regulation 28(1) reports of the Water Supply (Water Quality) Regulations 2016 (as amended) (‘the Regulations’) from the company which state that there is, or has been a significant risk of supplying water from multiple sites (see Annex 1) (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
Inability to verify disinfection.	C001 – Total Coliforms (confirmed)	Multiple hazard lines, for example: West Wickham TMS-4-T01U.179-MDCT004-T01U.179-C001
Inability to verify disinfection.	C002 – E. coli (confirmed)	Multiple hazard lines, for example: West Wickham TMS-4-T01U.179-MDCT005-T01U.179-C002
Inability to verify disinfection.	C003 – Enterococci (confirmed)	Multiple hazard lines, for example: West Wickham TMS-4-T01U.179-MDCT006-T01U.179-C003

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 all processes within defined operating ranges with appropriate triggers, responses, and contingency procedures.
   Date: Ongoing for the duration of this Notice
2. Continuous monitoring of raw and treated water with control systems, alarmed operating limits and automatic shutdown as appropriate.
   Date: Ongoing for the duration of this Notice
3. Continue to implement company water quality response procedures for investigation of contraventions including process optimisation and reporting; consumer complaints procedures; event response procedures for event actions; and notification criteria.
   Date: Ongoing for the duration of this Notice
4. Continue to implement the company’s Site Operating Manuals (SOMs), defining normal operating ranges, triggers, response, and contingency procedures, with controlled updates and review programmes. Implement the company’s Internal Waiver Process, where a deviation from the SOM is identified.
   Date: Ongoing for the duration of this Notice
5. Ensure that the Site-Specific Disinfection Policies remain up-to-date and implemented.
   Date: Ongoing for the duration of this Notice
6. Maintain contingency plans to protect human health in the event of a risk associated with drinking water quality, which should include liaison with local authorities and UKHSA to agree any actions needed to protect human health and issuing of advice to consumers, where required.
   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:

1. Conduct a comprehensive study to identify the technical, operational, and regulatory requirements for verifying disinfection at sites listed in Annex 1. To Include as a minimum:

• Review existing disinfection infrastructure and monitoring capabilities.
• Identify gaps in disinfection verification.
• Assess site-specific constraints.
  Date: 30 April 2026

2. Following (b)1, develop a phased programme of work to ensure that disinfection can be continuously verified at sites listed in Annex 1.

• Produce a technical report summarising verification requirements per site.
• Produce a risk-based prioritisation delivery matrix.
  Date: 28 February 2027

3. Complete Phase 1: Higher-risk sites as shown in Annex 1, Table 1 of this notice.
   Date: 31 March 2028

4. Complete Phase 2: Medium-risk sites as shown in Annex 1, Table 2 of this notice.
   Date: 31 March 2029

5. Complete Phase 3: Lower-risk sites as shown in Annex 1, Table 3 of this notice.
Date: 31 March 2030

(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 December 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 from multiple sites listed within Annex 1, 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:

1. Provide a progress report annually.
   Date: by 31 January each year.
2. Confirm completion of the study to identify the requirements of sites in Annex 1, as specified under measure (b)1.
   Date: 31 May 2026
3. Submit the programme of work for the sites listed in Annex 1 as required under measure (b)2.
   Date: 31 March 2027
4. Provide reports detailing the completion of the Phase 1 sites as shown in Annex 1, Table 1 of this notice, as per the requirement of (b)3.
   Date: 30 April 2028
5. Provide reports detailing the completion of the Phase 2 sites as shown in Annex 1, Table 2 of this notice, as per the requirement of (b)4.
   Date: 30 April 2029
6. Provide reports detailing the completion of the Phase 3 sites as shown in Annex 1, Table 3 of this notice, as per the requirement of (b)5.
   Date: 30 April 2030
7. Submit the audit strategy for auditing the effectiveness of the measures, as specified in measure (c)1.
   Date: 31 January 2026
8. Submit any revisions of the audit strategy produced under measure (c)2.
   Date: Within 1 month of a revision
9. 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
10. Submit a satisfactory completion report accompanied by a revised regulation 28(1) report with Board level Director sign-off.
    Date: 30 April 31

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
23 October 2025
Reference: TMS-2025-00003 v1

Annex 1 TMS-2025-00003 v1: Affected Assets and their Associated Risk Assessment References

Table 1: A list of higher risk assets affected alongside the associated risk assessment records and supply systems.

Asset Name	Asset Code	Associated Supply System and Reference Number	Completion Date
West Wickham works	T01U.179	YTMS1167 Addington Supply System YTMS1192 Farnborough Supply System YTMS1206 Knockholt Supply System YTMS1231 Westerham Supply System YTMS3000 Bromley Common, Bromley Inset (SSE) (TW Community; Farnborough)
Playhatch works	T06U.628	YTMS1217 Reading Supply System
Ashton Keynes works	T07U.722	YTMS1169 Ashton Keynes Supply System YTMS1225 Swindon North Supply System YTMS2003 Ashton Keynes Community
Millmead works	T04U.404	YTMS1195 Guildford Supply System
Watlington works	T05U.509	YTMS1179 Chinnor Supply System
Horton Kirby works	T01U.129	YTMS1193 Farningham Hill Supply System YTMS1222 Southfleet Supply System YTMS3015 Kent Wells (IWNL), Kent Wells (IWNL) (TW Supply system: Multiple) YTMS3021 Southfleet Community
Marlow works	T03U.336	YTMS1235 Wycombe Supply System
Orpington works	T01U.140	YTMS1192 Farnborough Supply System YTMS1206 Knockholt Supply System YTMS1231 Westerham Supply System YTMS3000 Bromley Common, Bromley Inset (SSE) (TW Community; Farnborough)
Clatford works	T07U.713	YTMS1208 Marlborough Supply System
Ashdown Park works	T07U.723	YTMS1168 Ashbury Supply System YTMS 1211 Newbury Supply System
Crayford works	T01U.107	YTMS1210 New Cross and Riverside Community YTMS1215 Oxleas Wood Community YTMS3004 The Bridge, Eltham Community YTMS3005 Heart of East Greenwich Inset Community – Subset of Hampton 30/36 Community YTMS3008 Greenwich Millennium Village Inset (IWNL) (TW Community: Hampton 30/36) YTMS3021 Kent Wells (IWNL), (TW Supply system: Multiple)

Table 2: A list of medium assets affected alongside the associated risk assessment records and supply systems.

Asset Name	Asset Code	Associated Supply System and Reference Number	Completion Date
Enborne Grange works	T06U.632	YTMS1211 Newbury Supply System YTMS2002 Newbury Community
Axford works	T07U.721	YTMS1208 Marlborough Supply System YTMS1225 Swindon North Supply System YTMS1226 Swindon South Supply System
Speen works	T06U.613	YTMS1211 Newbury Supply System YTMS2002 Newbury Community
Wantage Manor Road works	T06U.601	YTMS1230 Wantage Supply System
Seven Springs works	T07U.705	YTMS1181 North Cotswolds Community YTMS1212 North Cotswolds Supply system YTMS3011 Rissington Inset (Albion) (TW Community: North Cotswolds)
Lullingstone works	T01U.133	YTMS1176 Chelsfield Supply System
Bishops’ Green works	T06U.615	YTMS 1211 Newbury Supply System YTMS1217 Reading Supply System
Hungerford works	T06U.603	YTMS1204 Hungerford Supply System
Sundridge Works	T01U.160	YTMS1206 Knockholt Supply System YTMS1231 Westerham Supply System
Brantwood works	T01U.170	YTMS1167 Addington Supply System YTMS1218 Russell Hill Supply System YTMS3001 New South Quarter, Addington Community

Table 3: A list of lower risk assets affected alongside the associated risk assessment records and supply systems.

Asset Name	Asset Code	Associated Supply System and Reference Number	Completion Date
Bedwyn works	T07U.719	YTMS1204 Hungerford Supply System
Bibury works	T07U.718	YTMS1181 North Cotswolds Community YTMS1212 North Cotswolds Supply system YTMS3011 Rissington Inset (Albion) (TW Community: North Cotswolds)
Bradfield Works	T06U.620	YTMS1211 Newbury Supply System YTMS1217 Reading Supply System
Childrey Warren Works	T06U.602	YTMS1230 Wantage Supply System
Dancers End Works	T05U.503	YTMS1229 Tring Supply System
Greys Road Henley Works	T06U.626	YTMS1200 Henley Supply System
Hampden Bottom Works	T05U.504	YTMS1170 Aylesbury Supply System YTMS2001 Aylesbury Community YTMS3014 Aylesbury Supply System
Harpsden Works	T06U.627	YTMS1200 Henley Supply System
Haslemere Works	T04U.403	YTMS1232 Witley, Chiddingfold and Dunsfold Supply System
Hawridge Works	T05U.505	YTMS1170 Aylesbury Supply System YTMS1229 Tring Supply System YTMS2001 Aylesbury Community
Leckham-pstead Works	T06U.633	YTMS1184 Compton Supply System
Marlborough Works	T07U.708	YTMS1208 Marlborough Supply System
Mousehill/ Rodborough Works	T04U.402	YTMS1232 Witley, Chiddingfold and Dunsfold Supply System
Pangbourne Works	T06U.630	YTMS1217 Reading Supply System
Ramsbury Works	T07U.706	YTMS1208 Marlborough Supply System
Syreford Works	T07U.703	YTMS1212 North Cotswolds Supply system
Witheridge Hill Works	T06U.625	YTMS1182 Cleeve Supply System
Woods Farm Works	T06U.619	YTMS1223 Streatley Supply System