Same happened here. Over the period of 6 months I noticed water stains on the ceiling of first floor laundry room. Above the water stains was our 2nd floor shower and sink. Called "Woodbridge Plumbing" they came the next day. Took him less than an hour to cut several 12" squares out of 2nd floor dry walls to find water pipes going to shower and sink. With 3 tries he hit pay dirt. A solder joint on a copper pipe has a pin hole and was squirting water. The water was accumulating on the ceiling below. He re-solder the leaking joint in less than 30 minutes.