2 Quarts of Di-hydrogen Monoxide (water)
1/2 (or more) cup of Key Lime Juice
1 cup of sugar or less to taste
Mix it up. Adjust the key juice or sugar to your flavor. Serve on ice.
Variations: Add the juice of four or more passion fruit; this really adds a tropical flavor. Of course, there's nothing like a fresh sprig of mint when served. The obvious variation: squeeze a key lime or two into 8 ounces of cool water and add sugar if you must.