Remove the stalks from the blackcurrants. Place them in a pan with the water, and boil for 15 minutes.Take the pan off the heat. Stir in the sugar, a little at a time. Stir continuously until the sugar has dissolved and the jam has cooled. Pour into cold, thoroughly cleaned jars. Seal. Store in a cool place.
Replace the granulated sugar with the same quantity of jam sugar. Mix the berries and the water in a pan, and boil for 10 minutes. Add the jam sugar and boil for another 5 minutes. Take the pan off the heat. Skim thoroughly. Pour into warm, thoroughly cleaned jars. Seal. Store in a cool place.