If the groundwater is not potable because of e.g. arsenic or pesticide contamination, I think that homeowners are usually aware of that and therefore are more likely to use the water only for washing purposes.
The HOA where the condo is has an on-site water sanitation facility which recycles toilet, shower, sink water.
They don’t consider the recycled water potable, but I guess they consider it safe enough for watering plants, for re-use in toilet water, etc.
TLDR: in the above case, it’s bacterial risk or the use of a water sanitization facility that doesn’t provide guarantee around portability.
My earlier comment was motivated by a concern that tapping a non-potable water source for one’s own family might bear health risks without more analysis of the state of that water. For all you know, even if you only use that water for plants, maybe you’re growing food with water high in arsenic and it’s accumulating in the food.