It's always interesting and puzzling getting to know a new snake. None of mine (5) have ever sat in their water dish for longer than a few minutes but, like everyone here has said, there's many reasons a snake would choose to do so. Snakes have a lot of individuality to their personalities I find. Mine are all pretty different from each other.
Have you got the temperature, humidity, hides and such at their optimal conditions? Search this forum for corn snake care sheets and read up on how to keep snakie happy if you have not already done so. This will certainly help to boost your confidence in caqring for your new pet.
With research and attention to detail, you'll figure out the mystery soon enough I'm sure.
Folks here are happy to answer questions.
Welcome and good luck!