Juice your lemons and pit your cherries however you like. A cherry pitter is handy but not required if you're fine with a knife.
Make your simple syrup by combining your cup of sugar and one cup of water in your sauce pan. Bring it to a simmer for 3-4 minutes until the sugar is fully dissolved, then let it sit to cool.
Add your cherries to a blender or container and blend them until pureed. Be thorough; you want as much juice as possible.
Strain your cherry juice to remove the skin and pulp. I had to strain twice, using a rubber spatula to work it through. If you don't mind a little pulp, one strain is fine.
Mix the simple syrup, lemon juice, cherry puree, and remaining three cups of water, and stir or shake to combine. Add a bit more water if you like, it's your choice.
Chill or serve immediately over ice.