It is important that any substance that comes into contact with drinking water as part of the treatment process or in the distribution system is suitable for this use and does not cause contamination of the water supply. For this reason, Scottish Water and its contractors are required to use only products or processes that are approved for use in accordance with Regulation 33 of The Public Water Supplies (Scotland) Regulations 2014. The approvals process is administered for the whole of the UK by the Drinking Water Inspectorate (DWI) in England and Wales. In Scotland it does so on behalf of Scottish Ministers. Further information about the approvals process may be found on the DWI website (Regulation 33 in Scotland is the equivalent of Regulation 31 in England and Wales).
The list of approved products and processes is published annually. The current list may be found here.