Just because rain falls from the sky does not mean it is safe. In each stage of collection, storage, pumping and filtration safety considerations must be closely adhered to.
If we have a non-potable system, we need to ensure it is labelled as such, and that unsuspecting people do not have easy access.
If it is a potable water system then we need to test the water upstream and down stream of the filtering system, we need to ensure there is a maintenance manual and that a schedule of servicing filters is followed. Just as if you had a well, we recommend a yearly water test to ensure all is good.