Cut away the ends of the rhubarb and then wash them
Use a mandoline or similar to quickly slice the rhubarb into smaller pieces
Place rhubarb together with water and sugar in a pot and bring to a boil
Simmer for 10 minutes
Pour the rhubarb mixture through a fine sieve, pressing out as much liquid as possible. Let the liquid cool. Don't discard the rhubarb leftovers since it is really delicious to eat as it is or with some ice cream!
Mix rhubarb liquid with 500 ml cold water and the liquid of 2 lemons
Serve with ice cubes or even better with frozen pieces of rhubarb