We'll gladly taste every non-alc vigin margarita we come across, so very happy to share this one sent by our friends at Bittermilk in Charleston. This one uses their Grapefruit Margarita mix, which you can find in most stores around the country and online.
2 parts grapefruit Margarita (try to locate some of Bittermilks BarCoop Bevy brand)
1 part Sparkling water
Jalapeno slices (seeds removed!)
In a shaker, add Grapefruit Margarita and jalapeno slices with lots of ice.
Shake, and strain over ice in a tall glass.
Top with soda water
Garnish with a grapefruit peel.