Method

Place tap water, sugar & rhubarb into a saucepan over a med heat & cook until soft, then set aside to chill in the fridge.

Place all ingredients into a food processor or liquidiser & blitz smooth.

Place a fine sieve lined with a sheet of muslin cloth over a bowl, tip pulp into the sieve & push out juice with the back of a spoon or ladle to extract as much of the juice concentrate as you can, then twist muslin cloth to squeeze the last drop of the juice.

Pour juice concentrate into a jug with the tonic water & some ice & serve.