Problem is that with a 2 pole you will need two magnet poles or groups of magnets that make up poles, with a 4 pole motor you will need 4 magnets or groups of magnets but you'll get the same output at half the speed of a 2 pole, and a 6 pole will provide the same out put at a third the speed of the 2 pole. So while it may in
fact work you may need to use a belt to speed it up for a 2 pole to provide what you need, where you may be able to drive a 4 or 6 pole directly ( or at a lower ratio). Of course there are still unknowns here as to just how much water were talking about and how far it's dropping, the farther the more power available.
You need to determain the fall ( drop) and GPM available.