In my friends house all taps leave behind a green/blue residue overnight if one of the kids or a visitor fails to turn the taps off completely. (The taps "will" turn off properly but have "fashionable" small smooth handles so a good grip is required to make sure there are no drips.)
All the plumbing system is High pressure with no loft storage tank and the stain comes from both hot and cold taps.
See photo
It is a hard water area with one of these disposable cartridge conditioners (similar to but not exactly this)
fitted in the rising main near the stop c*ck.
My house is less than 400 yards away so I assume it has the same water supply, it does not suffer this problem, but I do have a low pressure feed to all except the kitchen sink.
Is this anything more than a minor irritant or is something seriously wrong.