Information Letter

DWI Information Letter 03/2005

24 January 2005

To: Board Level and Day to Day Contacts of Water and Sewerage Companies and Water Companies in England and Wales

Dear Sir or Madam

GUIDANCE ON THE CALIBRATION AND ANALYTICAL QUALITY CONTROL FOR RESIDUAL CHLORINE MEASUREMENTS.

Background

1. Water companies in England and Wales are required to analyse for residual chlorine in the water leaving water treatment works, in service reservoirs and at consumers’ taps in accordance with the requirements set out in the Water Supply (Water Quality) Regulations 2000 in England and 2001 in Wales (the Regulations).
   
   
2. The is no numerical standard for residual chlorine but water companies still have to meet the requirements of regulation 16(2)(e) in terms of the analysis. The Inspectorate issued Interim Guidance on the Regulations in September 2003, which included a section on the minimum performance criteria required for residual chlorine measurements.
   
   
3. Also in 2003, residual chlorine was selected as a parameter for the vertical audits of non microbiological parameters that were carried out for all companies. These audits were carried out on behalf of the Inspectorate by Dr Peter Whittle, Consultant. Dr Whittle produced a summary report of his findings, which was issued in May 2004 under the cover of Information Letter 7/2004. He expressed a number of concerns over the analytical control of residual chlorine measurements and he recommended that the Inspectorate should review the requirements and associated guidance accordingly.

Purpose

4. The purpose of this letter is to share with the industry the Inspectorate’s response to Dr Whittle’s recommendations. The Inspectorate has consulted with the industry on current best practice and recognises their concerns about over prescriptive regulation. The resultant guidance on calibration and analytical quality control for residual chlorine measurement, a copy of which is attached, takes account of Dr Whittle’s concerns and is intended to provide a pragmatic way forward for the industry.
   
   
5. The guidance is a stand alone document, which will be reviewed and revised at regular intervals and in the light of experience. The Inspectorate expects companies to take account of the guidance in formulating their procedures for residual chlorine measurements and to have suitable procedures in place by the end of June 2005.
   
   

Enquiries

6. Copies of this letter are being sent to Pamela Taylor, Chief Executive, Water UK; Richard Wood, Water Supply and Regulation Division, Department for Environment, Food and Rural Affairs; June Milligan, Environment Division, The National Assembly for Wales; Tim Hooton, Drinking Water Quality Regulator for Scotland; Randal Scott, Drinking Water Inspectorate for Northern Ireland; David Lowe, United Kingdom Accreditation Service; and Rowena Tye and Phillip Dixon, Office of Water Services.
   
   
7. This letter is being sent electronically to Board Level contacts. Please acknowledge receipt by email to dwi.informationletters@defra.gsi.gov.uk. Hard copies are not being sent but the letter may be freely copied. Any enquiries about the letter should be addressed directly to me.

Yours sincerely

Miss C R Jackson
Deputy Chief Inspector of Drinking Water

Attachment: Guidance on the calibration and analytical quality control for residual chlorine measurements