Water stains on ceilings and walls can be a symptom of a problem that needs attention. Blistering or peeling paint and yellow or brown spots are all caused by chemicals in the wall material reacting to water that shouldn’t be there. Inspect your roof, attic, gutters, windows and siding to find the source of the leak. An interior leak from a toilet or plumbing pipe could also be the culprit. Once you’ve fixed the problem you should clean the area with warm soap and water let it dry and apply a good sealant before painting over the surface.