In a large jug, mix the juice and grated lemon zest with the honey, grated ginger and caster sugar. Pour in 150ml soda water and leave to infuse for 10 minutes.
Top up with the remaining soda water. Using a fine sieve or piece of muslin, strain the mixture into another large jug, discarding the zest and ginger pulp. Chill in the fridge for at least an hour before serving with ice.