Remove the zest but not the underlying white pith from the lemons using a paring knife, vegetable peeler, or zester. [Editor's Note: This may amount to more zest than you've ever seen in a single place. That's okay.] Then juice the lemons. You'll probably end up with about 1 1/2 cups juice.
Place all the zest and juice in a saucepan, add the sugar and water, and heat slowly over medium heat, stirring constantly, until the sugar has dissolved. The liquid should approach boiling but should not actually boil.
Remove the pan from the heat. Strain the mixture and discard the lemon zest and any seeds. You should have about 4 cups concentrated lemonade syrup. Let it cool slightly.
Meanwhile, sterilize a large glass bottle and its stopper however you choose. (The authors like to thoroughly wash and dry the bottle, place it in a cold oven, and heat it to 320°F. After 20 minutes, they turn the oven off and let the jars cool slightly.)
Pour the warm lemonade syrup into the bottle and let it cool. Cover the bottle and stash it in the fridge until it's chilled through and up to several weeks.