Rainwater from the roof

I recently purchased the GSS2-IMP for my part-time home in Hawaii. It is safely stashed away against the possibility that the piped water supply is cut off (hurricane, power outage, etc.).
My plan is to catch rainwater from my roof which is the usual asphalt shingle construction (appx two years old).
 Please confirm that the unit will successfully and safely filter roof-caught rainwater including removing whatever petroleum products may leach out of the shingles and become a part of the runoff.

The GSS2-IMP will be extremely efficient at making the water potable and free of micro-organisms, particulates, and carbon based chemicals, such as petroleum products. If you want to filter further, consider two  CN-B2 2"x4" heavy-metal reduction elements to add on to your system. They can be purchased at the following link for $ 24.00 ea http://doultonusa.com/HTML%20pages/ceramic_candles_gravity.htm.