s9896:

If the leak actually came from the concrete ceiling as water drips, more than likely it could be "lime" or calcium carbonate, a water soluable mixture emitted by concrete.

Try to use a simple lemon - one you buy in a grocery store. Citrus acid will "dissolve" calcium carbonate, and will not damage your paint. It might remove the wax that might be on the paint, but not the paint iteself.

Try this first, as it is a cheap fix. If this does not do it, then it is not calcium carbonate, and you may have to spring for the clay......Andras