These are notes for the H2O Cocktails seminar at Tales of the Cocktail in New Orleans.
I think this concept was pioneered by Kathy Casey, one of the seminar hosts.
So, what are these H2O cocktails? Basically they're vodka drinks made with flavored water (not juice, no chunks) and no sugar. They come out to about 80 calories, all from the vodka. The waters used are infused with fresh ingredients, not commercial flavored waters.
They retain the craftsmanship of a fresh muddled cocktail, and recommended being mixed with flavorful vodkas.
Ultimately, I'm impressed with the concept. The drinks taste refreshing; they could be spa cocktails. They don't have the booziness and texture of a Manhattan, for example, but are more along the lines of a mojito.
To make a water infusion, either soak well-chopped fruit/toasted spices/other ingredients overnight in cold water, or consider doing a flash infusion with an isi nitrous canister.