New or modified plumbing can give your water an unusual taste or odor. This is caused when traces of copper and other materials come into contact with your water. This will usually improve with time as a thin protective layer of natural scale forms on the new plumbing, sealing the copper.
Tap or stopcock washer rubber causes an odd taste or odor, particularly if taps or stopcocks are new, old, or haven’t been used for some time. You will usually only notice the odor or taste when you use the particular tap causing the problem (unless it’s the stopcock, which will affect every tap). You may need to replace the washer, if the washer has been damaged because of worn tap seating, you will need to replace the tap seating too.
Flexible braided metal hoses are often used in modern plumbing, usually to make connections under the sink. The rubber or plastic lining inside them can sometimes cause an antiseptic taste. If the flexible hose is part of your drinking water plumbing, you may need to ask a plumber to replace the hose with an alternative type of hose that does not contain rubber.