I live in San Jose, CA in a 10-year old home with concrete slab foundation.
I noticed wetness in the carpet in the guest closet. The closet is in the middle of the first floor and far away from any tap/faucet/bathroom.
I removed the carpet and found that the floor is wet.
After thoroughly mopping and cleaning the floor, I let it dry for two days.

I notice that a small area (about 6" diameter) is always wet.
The walls and ceiling are all dry.

What could be the problem that is causing water leak in the floor? More importantly, what kind of financial damage it will cause to my family. I am already struggling with huge medical bills for my sick son and I am concerned about the cost of this repair

Also, are these issues covered by warranty from the builder? The house was built in spring 1998.