Make the syrup: 

1. To a small bowl, add the sugar and lemon zest. Using your fingers, massage the sugar and zest together until fragrant and evenly incorporated. 
2. To a small saucepan over medium low heat, add the diced peaches, sugar and zest mixture, and water. Cook over medium low heat and simmer for 15-20 minutes, until the peaches have softened and begin to break down. You'll want to mash them a bit throughout the cooking process using a wooden spoon or similar utensil.
3. Strain the cooked syrup to remove the solids, using a spatula or spoon to extract as much liquid as possible. Save the leftover peaches! They're basically like a jam.
4. Move the syrup to the refrigerator to cool completely. 

Make the soda: 

1. To an ice-filled glass, add anywhere from 2-4 tablespoons of the peach syrup (depending on your preferred level of sweetness). Top with sparkling water and enjoy!
2. To make it a dirty soda, blend up 1/2 of a peach with about 1/4 cup of water, then strain to make peach juice. Add 2 tablespoons of peach syrup to an ice-filled glass, then top with 1/4-1/3 cup of peach juice, then top with sparkling water and about a tablespoon of heavy cream or coffee creamer. Stir and enjoy!