I know our water and sewer authority publishes a report on water quality each year, but I don't remember seeing lithium content in the report.
The spring is privately owned. Here it is on google street view [1]. Lithia Springs gets their tap water from from the Dog River Reservoir in the southern part of Douglas County.
[1] https://www.google.com/maps/@33.8005688,-84.6403093,3a,75y,1...
I grew up in Cedartown, where the natural spring is also the town's water supply, so I just assumed it would be the same for Lithia Springs.
Not too surprising: I've done some poking around looking for datasets measuring lithium in drinking waters (the existing epidemiological work is, IMO, surprisingly small-n for something that seems to be routinely measured by drinking water systems), and it's pretty hard to find any lithium measurements.