Put washed clean redcurrants (no need to de-stalk them) in a saucepan with the water and bring to a boil for ten minutes.
Strain through a muslin lined sieve or jelly bag into a clean saucepan. Do not push or squeeze fruit to get the juice out just leave to strain naturally (otherwise it'll go cloudy).
Add sugar and, if you like, some cinnamon. In the original recipe it says 180g per 500g currants - but I used about that for 2kg of fruit!
Skim any froth or scum that comes to the surface and boil for a couple of minutes until the sugar is dissolved.
Pour through a funnel into a sterilised bottle. (Sterilise by washing and then placing in an oven at 120°C (240°F, gas 1) for 5 minutes - or put through a dishwasher.)
Keep in the fridge.