Hey Mikey,
Our biggest enemy is evaporation and it takes it's toll. As you know for most of California the rain pretty much turns off in May and doesn't restart until November (with an occasional odd storm thrown in for good measure). There is a balance between making a pond deep enough to allow for a decent sized pond after evaporation takes it's toll and yet keeping the pond a useable depth without steep sides.
It is not unusual for a pond here in California to drop 6 to 7 feet in a normal year. Bad drought years can be brutal. I've watched my pond drop a third or more in size.
The key to this entire issue is knowledge. There are state regulations and regulations by county. Focus on what counties that you might want to own a home in and learn all you can about their regulations.
DIED and Pond Frog have much more experience about this stuff than I do.
I went the easy route. I searched for quite a while until I found a property that already had a pond on it. That way I could focus all of my mistakes on managing the pond rather that waste my mistakes on constructing a pond first.
