1. Place the blueberries and water in a medium sized saucepan on medium heat.
2. Bring to the boil and mash fruit with a potato masher. Reduce heat.
3. Add lemon juice and Jam Sugar stirring until it has dissolved. Do not boil.
4. Keep stirring, increasing the heat until it starts to boil. Start timing and boil for 4 minutes.
5. Remove from heat and pot into warm jars and cover.