UK tap water does not have anything that can be detected unless the system has gone 'wrong'. If you are worried about your water supply, do ask your Supplier to come to the house and do free tests!!!! It will tell you on the appropriate web-site if there has been a problem.
ALL water supplied to householders, unless from a certified Spring or pump, has been treated. Again, if you look on the appropriate web-site you will find details. If your supply is un-cholorinated, you may well end up with Legionellas Disease!!!