Rain Harvest Sediment Filter and Barrel Storage

We have a well pump that irrigates our 1/2 acre property from a ready supply of the San Joaquin River. I would never want to drink this water, but with the current drought I have also become more aware of just how important water is to quality of life in California. Of course, the state has been in a drought perhaps the majority of years of my life, so to better appreciate the water that falls in form of rain, I'm going to capture some of that which falls on the asphalt shingle roof of my garage. If I can harvest and store for the middle of summer a hundred gallons of water, maybe the irrigation pump will burn a little less electricity...