Stir 8 cups water, sugar, 1/2 cup tamarindconcentrate, and 2 tablespoons lime juicein large pitcher until sugar dissolves.DO AHEAD: Cocktail base can be made1 day ahead. Cover and refrigerate.
Combine 1/2 cup cocktail base, 3tablespoons vodka, 2 teaspoons tamarindconcentrate, and 1 teaspoon lime juice incocktail shaker.
Add 1 cup ice cubes; shake30 seconds to chill. Strain into 2 Martiniglasses.
Garnish with lime slices. Repeat3 more times for 8 cocktails.
* Often labeled "concentrate cookingtamarind, "tamarind concentrate canbe found at Thai and Asian markets.
