I like this drink a lot, so I always have some in the refrigerator. I like mine pretty sour, but of course you can add more sugar.
6 limes (1/2 C juice)
6 T sugar
3 1/2 C water
1. Cut limes in half and squeeze juice through a strainer.
2. Pour lime juice into a 1L (1 quart) Nalgene.
3. Add sugar.
4. Fill the Nalgene most of the way full with water (about 3 1/2 C) and shake.