Drinking Water Inspectorate: Information Letter 16/99 - 20 December 1999
To: Board Level Contacts of Water and Sewerage Companies and Water Companies in England and Wales
Dear Sir/Madam,
The Water Supply (Water Quality) (Amendment) Regulations 1999: Cryptosporidium in Water Supplies
Purpose
1. The purpose of this letter is to advise water companies of the Inspectorate’s interpretation of “sufficient treatment plant capable of continuously removing or retaining particles greater than 1 micron diameter” and some associated matters.
Background
2. The Guidance on Assessing Risk from Cryptosporidium Oocysts in Treated Water Supplies (“the Guidance”) associated with the Water Supply (Water Quality) (Amendment) Regulations 1999 (“the 1999 Regulations”) includes the following:
“2. Risk Assessment
1.1 Water companies must carry out a risk assessment for each of their water
treatment works taking into account the factors listed in Annex A. However, for the purposes of the Regulations, the Secretary of State considers that the following water treatment works should in all cases (other than 2.2 below) be classified as constituting a significant risk.
- i.) Direct abstraction or with average storage of seven days or less from a river or stream.
- ii.) Evidence of rapid river or surface water connection to the aquifer demonstrated by the confirmed presence of faecal coliform bacteria in the raw water.
- iii.) Past history of an outbreak of cryptosporidiosis associated with the water supply where the reason is unexplained and no specific steps have been taken to prevent a recurrence.
2.2. Any treatment works, in which all water passes through sufficient treatment plant capable of continuously removing or retaining particles greater than one micron diameter and where this process is subject to continuous monitoring and shutdown or turn out on failure, will not require continuous monitoring irrespective of other factors, including 2.1 (i), (ii) and (iii) above.”
3. Some companies are considering the use of membrane and other filtration systems to meet the requirement of paragraph 2.2 above and thereby avoid the requirement under the 1999 Regulations to install continuous sampling equipment.
4. A number of membrane and other filtration systems have been approved under regulation 25 of the Water Supply (Water Quality) Regulations 1989 (“the 1989 Regulations”) and these are listed in section 7 of the Secretary of State’s List of Approved Products. The Committee which advises the Secretary of State on approvals considers whether the use of a product will cause a risk to the health of consumers. The Committee does not consider fitness for purpose and listing of an approved product does not constitute an endorsement of the claims of manufacturers/suppliers.
5. It is for water companies to decide which membrane or other filtration systems to use so as to meet the requirement of the 1999 Regulations that the water entering supply from their treatment works contains an average of less than one Cryptosporidium oocyst per 10 litres of water. Of course, any system used must be approved under regulation 25 of the 1989 Regulations. However, if the membrane or other filtration system does not comply with paragraph 2.2 above, continuous sampling and daily analysis under the 1999 Regulations will be required.
6. In order to assess claims by water companies that they do not need to install continuous sampling equipment to monitor the effectiveness of the treatment process under the 1999 Regulations because they had installed, or were planning to install, treatment capable of removing or retaining particles greater than one micron diameter, the Inspectorate considered that it was necessary to have an independent assessment of the claims of manufacturers/suppliers in respect of the ability of their products to remove particles.
7. The Inspectorate commissioned the Laboratory of the Government Chemist (LGC) to carry out the review. LGC was asked to assess whether manufacturers/suppliers holding approvals for membranes and other filtration systems had provided evidence that their products were capable of removing or retaining particles with a diameter of greater than one micron. The LGC report cannot be made publicly available because some of the information provided by the manufacturers/suppliers is commercially confidential.
8. A number of manufacturers/suppliers have not made specific claims for removal of Cryptosporidium, or for removal of particles of a specific size. It was necessary therefore for LGC to consider whether the test data that had been submitted was adequate for the purposes of this review. LGC were asked to pay particular attention to whether the testing had been sufficiently rigorous, given the particular difficulties in performing Cryptosporidium removal studies at concentrations encountered in the environment. In reviewing the information provided by manufacturers/suppliers, LGC considered:
- (a) whether data from testing for removal of particles other than Cryptosporidium was relevant to this assessment;
- (b) whether membrane reliability had been addressed;
- (c) whether worse case scenarios had been taken into account and
- (d) whether experimental test design, including control experiments, was satisfactory.
9. In respect of 8(a) above the following test data were considered to provide satisfactory evidence for removal or retention of particles with a diameter of greater than one micron:
- - chloride ion or hardness ion rejection; or
- - removal of all Cryptosporidium oocysts; or
- - removal of bacteria, bacterial spores, bacteriophages or viruses.
In the future it is possible that other types of test data may also provide satisfactory evidence of one micron particle removal.
List of products capable of removing or retaining particles greater than one micron diameter
10. The Inspectorate has assessed the LGC report. The Inspectorate considers that on the basis of the evidence provided, the following manufacturers/suppliers have shown that the listed products, all of which have been approved under regulation 25 of the 1989 Regulations, are capable of removing or retaining particles with a diameter of greater than one micron.
Company Product AEA Technology Ltd Kerasep Cross Flow Filtration Module Fluid Systems Ltd TFC Membrane Elements Degremont UK Ltd Aquasource UF Membrane Module Kalsep Ltd Kalmem Polyethersulphone Hollow Fibre Element Koch Membrane Systems Ltd Targa Modules V and H US Filters Ltd CMF Continuous Microfiltration Systems M1/M2 and M10 PCI Membrane Systems Ltd PCI Membrane Filtration System – Spiral Element
PCI B1 Module and Membrane – Tubular Element 1
PCI Tubular C10 Module and Membrane System (incorporating Tubular Element 1)X Flow BV X Flow Membrane Filtration Elements 11. Products have not been included in the list in paragraph 10 above where claims from manufacturers/suppliers for removal of particles have been based on:
- (a) the physical characteristics of the material and the integrity of the
manufacturing process; or- (b) limited test data or inadequate experimental design; or
- (c) evidence that particles of a diameter of one micron or greater are not completely removed.
Any manufacturers/suppliers whose approved products have not been included in the list in paragraph 10 on these grounds may ask the Inspectorate for a review of their product if they submit additional relevant testing data. Any manufacturers/suppliers whose products have not been approved under regulation 25 of the 1989 Regulations will need to obtain such approval before the Inspectorate will consider test data for the removal of particles. The list in paragraph 10 will be up-dated when existing and new approved products have been demonstrated to the satisfaction of the Inspectorate to remove or retain particles greater than one micron diameter.
Integrity of membrane or other filtration systems
12. Paragraph 2.2 above of the Guidance requires the treatment process to be subject to continuous monitoring and shutdown or turn out on failure if it is to be used to avoid the requirement for continuous sampling under the 1999 Regulations. It follows that manufacturers/suppliers must include with their membrane or other filtration systems a system of monitoring to detect whether there is a failure of integrity of the filter barrier. Any significant failure of integrity must lead to cessation of supply of the affected water from the treatment works. In modular filtration systems it may be acceptable to remove just the failed module from supply provided there is a system for identifying accurately any failed module.
13. As design of membrane and other filtration systems varies widely between different manufacturers and suppliers, the Inspectorate is not able to give detailed advice on integrity testing. The Inspectorate understands that systems based on bubble tests under pressure or vacuum and systems based on challenge by inert particles and monitoring turbidity or particle count/size may be suitable. Ideally there should be continuous monitoring of integrity using these techniques but the Inspectorate recognises that this may not be practical for some techniques. Intermittent monitoring at an appropriate frequency based on system design and risk of failure may be acceptable. Other options that water companies or manufacturers/suppliers wish to put forward would be considered by the Inspectorate (see paragraph 14 below). Where automated monitoring systems are installed, these should be linked to a control room by telemetry with appropriate alarms when failure of integrity of the filter barrier occurs.
14. Water companies proposing to install membrane or other filtration systems to avoid continuous sampling under the 1999 Regulations should ask the manufacturers/suppliers to provide full details of their system of monitoring the integrity of the filtration system and make an assessment of whether that is adequate for the system design and the circumstances at the treatment works. Water companies are required to include in their submission to the Inspectorate on the programme for implementation of regulation 23(B)(1) of the 1999 Regulations, details of the system to be used for monitoring the integrity of the membrane or other filtration systems that they propose to install.
Enquiries
15. Any enquiries on this letter should be addressed to Anthony Lloyd (020 7944 5959).
16. Please acknowledge receipt of this letter using the attached slip and reply paid envelope.
17. Copies of this letter are being sent to Pamela Taylor, Chief Executive, Water UK; Bob Dinwiddy, Water Supply and Regulation Division, Department of the Environment, Transport and the Regions; Bob Macey, Environment Division, The National Assembly for Wales; Tim Hooton, Water Services Unit, Scottish Executive; Randal Scott, Drinking Water Inspectorate for Northern Ireland; and Rowena Tye, Office of Water Services and to manufacturers/suppliers holding approvals for membrane or other filtration systems under regulation 25 of the 1989 Regulations.
Yours faithfully
Michael Rouse
Chief Inspector
Drinking Water Inspectorate
| A - Z Index | Business and Technical | Consumer Information | Contacting us |
| DWI Home Page | News | Product Approval | Search our site | Wales |
Drinking Water Inspectorate,
Floor 2/A1, Ashdown House, 123 Victoria Street, London, SW1E 6DE
Telephone : 020 7944 5956 - Facsimile : 020 7944 5969
E-mail: dwi_enquiries@detr.gov.uk
Updated 11 July 2001
Return to Current Information Letters Index
Return to Information Letters Index
Return to Drinking Water Inspectorate Home Page
Department for Environment, Food & Rural Affairs (DEFRA)Home Page
The National Assembly for Wales / Cynulliad Cenedlaethol Cymru Home Page
Web site terms
© Crown copyright 2001