Regulation 31 deals only with products used by water companies in the treatment and distribution of public water supplies.
PRODUCTS APPROVED FOR USE IN CONTACT WITH PUBLIC WATER SUPPLIES
In England, Regulations 31 to 33 of the The Water Supply (Water Quality) Regulations 2000 concern the introduction of substances and products (including construction products) and processes for use in the treatment and provision of public water supplies. They implement the requirements of article 10 of the European Union Directive 98/83/EC on the quality of water intended for human consumption, in respect to substances and materials used in the preparation and distribution of water, up to the point of delivery to premises.
Regulation 31 of the Water Supply (Water Quality) Regulations 2000 requires that water undertakers shall not apply or introduce any substance or product into public water supplies unless one of the requirements of this regulation is met. One of these requirements is that the substance or product has been approved by the Secretary of State for the Environment, Food and Rural Affairs or the National Assembly for Wales (collectively referred to as the Authorities), where there are similar provisions by Regulations 31 of The Water Supply (Water Quality) Regulations 2010. Similar provisions apply in Northern Ireland.
There is a separate legislative and approval process for Scotland. Further information on this can be obtained by contacting the Drinking Water Quality Regulator for Scotland, either by writing to Area 1-D South, Victoria Quay, Edinburgh,EH6 6QQ, or from the DWQR website - www.dwqr.org.uk.
The Drinking Water Inspectorate (DWI) operates the approval system on behalf of the Authorities. DWI accepts applications for approval of products used both before and at the treatment works, and in water distribution systems up to the point of delivery to premises.
When considering an application for approval, DWI considers only whether the use of a substance or product will adversely affect the quality of the water supplied, or cause a risk to the health of consumers. The DWI does not assess fitness for purpose and approval by the Authorities must not be taken as a favourable assessment of the performance or merits of any substance or product. DWI cannot advise on approval of products that will not be placed on the United Kingdom market.
Products approved for use in the treatment and provision of public water supplies under Regulation 31 are listed on the DWI website http://www.dwi.gov.uk/drinking-water-products/approved-products/soslistcurrent.pdf. It is important to distinguish between listing under the Water Regulations Advisory Scheme (conformity with the requirements of the Water Supply (Water Fittings) Regulations 1999) and approval under Regulation 31. The Water Regulations Advisory Scheme (WRAS) is concerned with products used after the time of supply, when water has passed into the consumers’ pipes/buildings. Regulation 31 deals only with products used by water companies in the treatment and distribution of public water supplies.
Many products have been tested against the requirements of both schemes and are listed in Parts 1, 2 of this directory and on the DWI website. Further information about the regulatory approval system and how to apply for approval, can be obtained from - Regulation 31 Enquiries, Drinking Water Inspectorate, Area 7e, 9 Millbank, c/o Nobel House, 17 SmithSquare, London, SW1P 3JR. Tel: 030 0068 6400 or from the DWI website - www.dwi.gov.uk/
 and combined licensees, see The Water Act 2003 (Consequential and Supplementary Provisions) Regulations 2005
 Regulation 30 of the The Water Supply (Water Quality) Regulations (Northern Ireland) 2007.
 Regulations 33 of the The Public Water Supplies (Scotland) Regulations 2014