Wash the ginger and grate into a medium sized bowl (there is no need to peel first).
Add the lemon zest, coconut sugar and rosemary and using a pestle, bash the ingredients together until they have released their juices and are fully softened (about a minute).
Add the lemon juice and half the water to the bowl and stir thoroughly. Pour the liquid through a sieve and press down firmly ensuring all the liquid is squeezed out from the pulp.
Fill a jug with ice, pour in the juice and add the remaining water, give it a quick stir and serve. We like to garnish with extra rosemary.