Customer had spot on ceiling beneath master bathroom shower. Customer was unsure if watermarks had been there for a long time or just recently. Cut and diagnosed potential leak and found P-trap for master shower directly on drywall ceiling. Old watermarks coming down both sides of P-trap were evident. Ran shower for approximately 15 minutes with no water coming from slip joint or from shower drain. Advise customer of what would be necessary to replace P-trap. Gave estimate for water heater replacement.