This is really more like a weak lemonaide, but we call it lemon water. It is quite refreshing. We serve it at every wedding, party, gathering. You can get citric acid from a restaraunt supply but I think it is to expensive there, so I buy it online. However, the lemon extract is way cheap at a restaraunt supply.
9 cups sugar
4 tablespoons citric acid (1/4 cup)
4 teaspoons lemon extract
5 gallons water
Mix all together, add a bunch of ice and some lemon and/or lime slices. The lemons and limes are not necessary, but they definately add to the presentation.