Mark:
Your question is limited, you need to define what the Banki can produce and the RPM, then I can tell you what would be the best generator for your project.
So please inform about the water volume, the head the diameter for the Banki and what is the RPM you are designing for.
Alternators for cars or motorcycles are designed for high RPM, a Banki is designed, generally, for low RPM,
Regards
Nando