Please help!

Our house is about 105 years old. We just started noticing that all the cold faucets upstairs are dispensing dirty cold water. (The hot water faucets are fine.) This is affecting our toilet, bathtub, and sink. Downstairs faucets do not seem to be affected.

My husband did clean out the bathtub drain because it was running a little slow, but this did not help at all.

What could be causing this?