mine prefer Gerolsteiner deutches mineral wasser.
but seriously, why add co2 to soil? leaves use co2, roots use o2. foliar feed if you do try it and see what happens
Actually, the roots use both o2 and co2, the leaves use co2 mostly, with fractional amounts of o2 used.
Plants roots use about equal amounts of both believe it or not, so adding co2 would provide some effect, but my guess is that the co2 levels will fade gradually over a few hours after watering, not exactly good constant source for co2, but with the added mineral content in the mineral water, I imagine it would provide some benefit.
Not exactly cheap, but if you demand purity I feel Perrier isn't a bad choice, might be worth it to you.... test it out on one plant only* and see how it goes, good advice for any new test ideas or chemicals and such.