I have a cistern that collects rainwater. Water goes into a 10,000 gallon underground holder(cistern) that is divided in two by a cinderbrick wall. The water where the house intake has been filtered thru this wall. The intake is a couple of inches above the floor to avoid settled crap. We have two Omni filters, the first a sediment filter, the second a carbon filter. They get changed every coupla months depending on. The unit is sealed, so the only "bad" thing that gets in it is bird poop and whatever nasty the rain water brings in. I throw in a cup or two of Clorox every once in a while when we expect rain(to mix it well.)
It's gotten so that I can't drink water at most restaurants because of the chlorine taste.
http://www.omni-water-filters.org/WFwholehouse_u25.htm