We're capturing all the water from the roof, more or less- and it's largely clean already, but we need two things:
A "first flush bypass" which should cause the first few gallons off the roof to bypass the main tank (taking the initial junk with it). The easiest way to do this is to have a dead-end direct pipe with a small drain- when that fills, it then shunts to the tank.
There is a sample here:
as well as one installed at charlotte energy solutions near cpcc, and area 15 in NODA.
Note ideally we'd like to retain even the first flush water for some purposes- perhaps subjecting it to additional filtering.
Here are some examples of different elements:
The first filter would also include some levels of screening to get any obvious particulate out without slowing the flow. It should be as close to maintenance free as possible, and shed debris naturally or with very minimal effort (i.e. tap it with a stick, as opposed to remove and rinse filter).