I tried this one this weekend and it is fabulous!!!! It was submitted by ssmithtrans at allrecipes.com

3 cups water
1 1/2 cups fresh lime juice
1 1/2 cups cointreau
1 1/2 cups silver tequila
1 lime, cut into 8 wedges
coarse salt

Here is what you do…
Mix the water, lime juice, tequila, and cointreau in a half-gallon pitcher. Stir to mix.
Then just rub the rim of a margarita glass with lime, and dip in salt. Fill the glass with ice, and top with the tequila mixture. Decorate with a slice of lime.