Pour water into a saucepan, bring the water to a boil, drop a sprig of fresh rosemary into the hot water. 

Remove the saucepan from heat and cover with a tight-fitting lid; allow the rosemary to steep in hot water for five minutes.

Chill rosemary-infused water in the refrigerator until cool.

Cut the watermen into small chunks that will fit into the holes of an ice tray. 

Place a bit of watermelon into each of the holes of an ice tray. 

Fill each hole with water and place the ice tray into the freezer overnight.

Use in cocktails.