Looks like you have a young northern water snake, Nerodia sipedon. The main problem with your setup would be keeping it clean. You would need to remove the water, rocks and decor weekly for a thorough cleaning. Those pebbles are right around the perfect size for causing impaction on that snake too. Too large to pass easily but small enough to be ingested accidentally. An easier solution would be a typical terrestrial setup with a large enough water dish for soaking and feeding. You take him out with your hands, the snake can't hurt you. It will likely bite repeatedly and musk to no end - get used to stinky hands.