Cut the pumpkin into cubes, pour in the water and simmer for about 15-30 minutes or until the pumpkin becomes soft. Cool the pumpkin a little and beat it with a hand blender until smooth.
Add sugar and juice from half a lemon to the pumpkin. Return to the fire and bring to a boil.
Cook the jam to the desired density, stirring occasionally for about 30 minutes.
Pour the finished jam into sterile jars and roll it up.