“treated” it’s right there in the headline!

Seriously, tho…
https://news.ycombinator.com/item?id=37628900
Has some discussion on it.
Chances are, it’s the water from the pad protection (rain birds, noise dampening, the fix for the concrete being obliterated etc). Contaminants will be removed, it will be filtered etc…

The concern is around it being freshwater, and it upsetting the freshwater/saltwater balance in the area