Mash blackberries, lemon zest and juice, and water in a large pot over medium heat and bring to a simmer.
Add sugar, stir and mash the berries again.
Simmer for 20 minutes before bringing the mixture to a rolling boil.
Meanwhile, soak gelatin sheets in ice water until pliable.
When the berries comes to a boil stir gelatin sheets into the mixture and boil for an additional 3-4 minutes before bringing back down to a simmer.
Simmer for an additional 5 minutes, remove from heat and allow to cool completely.
Pour the jam into a clean canning jars and place in boiling water for about 10 minutes.
Remove the cans from heat, dry off and set aside to cool completely.
Place in the refrigerator until ready to use.