Cut the cucumber and rosemary (removing the stem).
Add cucumber, rosemary and 1/2 cup of water to your blender, processor, ninja, etc. Mix, blend, pulverize into a frothy liquid.
Measure how much your ice tray will hold. Fill it with water and pour into measuring cup. Note the amount and empty the measuring cup.
Pour the frothy liquid into the measuring cup and add water to fill to the amount your tray holds. You may want to stir or blend again at this point.
It is fine if the froth remains atop. Gently pour into ice tray.
Pop and save in freezer container. Add 1-2 cubes to your water or several in a smoothie. Enjoy!