Start by taking a small saucepan and adding 1 cup of the water and the sugar, stir, and boil stirring constantly until the sugar has dissolved for about 5 minutes. Cool this to room temperature. While you're waiting for it to cool you can juice your lemons with a citrus juicer, then stick that juice in the fridge while you're waiting.
Now Combine your remaining 6 cups of water with your sugar water and stir, Stick in the fridge until cool and ready to serve.
Notes
*If you hate any lemon pulp I would recommend taking a sifting strainer and straining the lemon juice through it before adding it to the water and simple syrup.