It had to have been the turtle water. The turtle carries a substance on his skin that can get you sick if it gets in your eyes or mouth. Who's to say the snake didn't go in the water for a swim. Sorry to hear that the snake died. Did the other snake go in the turtles tank? If so, you might want to take it to the vet.

It might not have been the turtle though. Like Steve said, nobody can really know what happened to the snake unless we have more details.

Again, sorry to hear about the death.