Put the rhubarb
in a bowl, pour over 4 cups boiling water, cover, and leave at room temperature overnight. Next day, strain the liquid into a saucepan
, discarding the rhubarb. Add the sugar
and lemon juice
, and bring to a boil 5 minutes. Cool. Taste, and add more lemon juice if necessary. Strain
into a bottle, and cork. Store refrigerated, to be served ice-cold.