Actually yes, they detected a deep aquifer near the mantle years ago that would have more water than the entire Pacific.

Also I started to question the fossil origin of oil when I learned about high-temp high-pressure methods of synthesizing it in college and wondered "so why doesn't that happen down deep in the crust?" To me coal is the only true fossil fuel as we find plant fossils in it all the time and I've seen them myself but given how on places like Titan it rains liquid methane and there are heavier hydrocarbons on the surface that clearly didn't come from rotting biomatter it makes you wonder.