I hope you mean 12 gallons per minute. That would work on a small pelton turbine coupled to a slow speed alternator (maybe 1200 rpm for 12 volts)
If you only have 12 gallons per hour you would need to either store and dump the water for a shorter period of time or be able to downsize the generator. Years ago I used a 3 watt bicycle generator with a metal shaped into many buckets pressed onto the end to produce a trickle of power.
Chris