Give us an idea of what your water flow rate is (for example galons/sec or any other units) and the water drop from the higher posible point to the lowest (water HEAD). The you can have an idea. Check my diary, I have a small creek and I am building a small hydro-generator to utilize next spring. If you are where lots if sun is available you may want to consider a solar cell also, I purchased one this summer (123 watts) that took care of all my lighting and computer needs + all day music (radio). It is high inital cost but almost zero maintenance.
Good luck, Wilson