Medicinal or TCP type tastes are usually traced to unsuitable or degraded tap washers, rubber tap extensions and other fittings, such as sealing rings in electric kettles and flexible hoses on washing machines and dishwashers.
If these have even very low concentrations of phenolic chemicals, traces can dissolve in water and react with the chlorine forming chlorophenols, including TCP.
Although these are not considered harmful, they can cause noticeable tastes and odours at extremely low levels.
A frequent cause of TCP taints in the water supply is the flexible cold water feed pipes on washing machines or dishwashers.
To check if an appliance connection is causing the taste issue, turn off the water supply to the appliance using the service valve at the point where the hose connects to the mains supply.
If the TCP taste disappears after running the tap for a short while when this valve is closed, this suggests that the flexible hose is the source of the problem.
The best solution is to have a one-way check valve fitted to the connector just before the flexible pipe to prevent backflow. Check valves are simple to install and can be bought from most plumbing merchants and DIY stores.
Some taps use flexible or braided hoses to connect the tap to metal pipes. Some of these may cause medicinal tastes. The best way to eliminate these is to ensure that all your drinking water fittings are approved.
If you have a second mains supplied tap in the house, try using water from this. If you notice no medicinal taste, then the cause may be a tap washer in the original tap.
Another cause of TCP taints in the water supply is the deterioration of materials from within your kettle, even when new. Always follow the manufacturer's instructions when using a new kettle for the first time.
If a TCP taste is only present in hot drinks, boil some water in a clean saucepan. If the taste is no longer apparent, it suggests that something in the kettle is responsible.