We always appreciate the chance to help folks. I'm certainly happy to
answer. Is it only the cold, or is the hot pressure similarly affected? If
it is, you might try taking the little screens off the faucet spouts to see
if they're clogged.
By the way, it's probably not calcium. It's more likely lime, manganese,
or just plain rust.
Mike (The polite plumber who respects the other gender after getting his
head bitten off a few months ago by some Amazonian princess warrior. Boy,
that broad really had an attitude!)