Add the fruit to a preserving pan with the measurement water. Bring to the boil, then reduce the heat and cover the pan. Simmer for 20–30 minutes, until the redcurrants are really tender.
Add the lemon juice and sugar and stir over a low heat until the sugar has completely dissolved.
Increase the heat and bring to the boil, then boil rapidly until setting point is reached (10–20 minutes). Remove the pan from the heat and skim with a draining spoon or stir in butter if needed.
Ladle into warm, dry jars. Cover with screw-top lids, or with waxed discs and cellophane tops secured with elastic bands. Label and leave to cool.
To serve, spoon over split scones topped with whipped or clotted cream.