Place peach halves in a glass baking dish, drizzle with the agave/honey and sprinkle the rosemary on top. Cover with tin foil and roast for 35 minutes.
Remove peaches from oven and let cool to touch.
Remove skin from peaches, it should come off easily after roasting and place the peaches with any accumulated juices from the baking dish in a blender. Blend until smooth.
Add the lemon juice and water and blend again until fully incorporated.
Pour the lemonade into a pitcher and refrigerate until chilled.
Serve with additional sliced peaches and rosemary sprigs.