redwood - I have had the question come up to me before too.
"why does the water taste different when coming from a new faucet?" I have observed almost a soapy sudsy condition coming from a new tap with a funny taste. This was not happening with the old. Aerator? Aerator in combination with residue from manufacturing? Pipe dope in the supply line? Very curious, especially months after install.
Follow-up conversations may have shed light on it. The sudsy condition is just the aerator the taste was possibly manufacturing residue but also psycho semantic. When something looks different it also seems to taste different when in reality it probably doesn't. The particular owner of that faucet doesn't taste anything unusual anymore (or they are used to it)