I’ve become a fan of flavored seltzer water. With flavors like lime, pomegranate, green apple and yes, even eggnog (at holiday time), one can never get bored. Also, thanks to seltzer, I’ve been able to wean myself off Diet Coke to some degree. But is carbonated water really all that good? And what’s the difference, anyway, between club soda, seltzer, and tonic water?