Stir the sugar and 2 cups of the water together in a small saucepan over medium heat. Cook, stirring occasionally, until the sugar dissolves and the mixture turns clear. Cool completely. This part can be done up to 2 weeks ahead and chilled in the fridge.

Use a blender or food processor to puree the strawberries. Strain them through a fine mesh sieve, if desired, to remove seeds.

Add lemon slices and 4 cups of ice to a large pitcher. Add the simple syrup, lemon juice, and strawberry puree. Add enough remaining water to get the lemonade to your desired strength. Keep in mind that as the ice melts your lemonade will be diluted.