Wash the juneberries thoroughly and remove any stems or leaves.
Add the berries to a large saucepan and gently mash them using a potato masher.
Pour in the water and lemon juice, then place the saucepan over medium heat.
Stir in the sugar and cook until the mixture begins to boil.
Add the fruit pectin and continue stirring for 2–3 minutes until the jam thickens slightly.
Remove the saucepan from heat and skim off any foam from the surface.
Carefully pour the hot jam into sterilized mason jars, leaving a little space at the top.
Seal the jars tightly and allow them to cool completely before storing.
