In a small saucepan simmer 1 cup sugar with 1 cup water to make a simple syrup. Once the sugar has all dissolved, stir in 1 cup lemon juice. I like to use fresh-squeezed because it makes me feel all homemakey (yes that is a word, I know because I invented it) but feel free to use bottled.
Dilute this syrup / lemon mixture with 3 to 4 cups of cold water – use sparkling water if you wish. Refrigerate until nice and chilled. If it’s a little too sweet for you, add more lemon juice. Enjoy!