However you are correct that it can be tricky. The problem boils down (ha ha) to where the water was collected from and where it will be used, and interconnection with potable water systems.
For example, collecting rainwater from streets, parking lots, and pavements is discouraged for potable use because of toxins. Rainwater from roofs and hard surfaces is deemed probably acceptable for potable use. Interconnection with potable systems will require a backflow valve to prevent rainwater from entering treated water system. Water for agricultural use does not have to follow the same guidelines.
Also mosquito and insect infestations must be addressed as well as possible micro organism contamination in potable supplies. Most older rural homes will actually have a cistern for water collection (mine does).
Generally it seems most of the regulations are common sense, and equivalent to the NEC electrical code.
Rainwater collection is encouraged in the Commonwealth of Virginia.
Thanks for the information.
It chaps my @ss when an official lies to me.