try making noise with the water bowl, say take your spray bottle n spray the water so that he hears the water n comes to investigate on his own. Or empty the bowl and pour water in slowly from higher up to make noise as well.

Steve has a good question as well, is it a small snake and a deep / tall water dish? What is the shape? Is the base / bottom wider like this ... /---\ or is the base narrower then the top like this ... \---/
(make those shapes /--\ and \--/ with your hands if you don't fully understand what I mean
The base should be wider then the top so they can kinda use it like an easy access ramp, otherwise if there is to much of a lip (top is wider then the base) then the snake may not realize they have to go 'up' for water and they may just circle around the bottom clueless because nature suggests water is normally down somewhere, not up.