Have you checked behind your sink or washer lately?
Do you ever look under you sink? All the way in the back behind the toilet paper and various cleaning products? What about pulling the washer away from the wall and looking behind that?
A lot of time you can have a water damage and not even realize it. That was the case in this job. Our customer had a leak in the wall behind his sink and didn't realize it until he tried to sell his home, and a home inspector found it, because it went unnoticed, mold grew and had to be fully re-mediated.
Leaks in the wall are hard to notice but there are some things to look for. Baseboard separation in one of the easiest things to spot. The baseboard swells up from the water and pulls away from the wall.
Peeling paint or paint flaking away. These are easy to see but a very good indication of a potential water leak.
Lastly, any sort of discoloration. If you are unsure if you have wet building material, call your local SERVPRO franchise for a moisture inspection.