In a saucepan, mix water, berries, sugar, lemon juice, and salt. Bring to a boil.
1 c. water, 4 c. fresh or frozen blueberries, 3/4 - 1 c. sugar, 1 Tbsp. lemon juice, 1/4 tsp. salt
Mix clear jel with water to make a slurry. When the blueberry mixture begins to boil, slowly pour in the clear jel slurry, stirring constantly, until thickened. Be careful, because the filling may splatter as it begins to boil.
1/4 - 1/3 c. clear jel mixed with approx. 1/3 c. of water
Remove from the heat and add the butter and cinnamon. Stir to combine.
1 Tbsp. butter, 1/2 tsp. cinnamon
Preheat the oven to 425°.
Pour the blueberry mixture into a prepared, unbaked, pie crust. Cover with a top crust or lattice strips.
2 (9") pie crust pastries for bottom and top
Brush the top with egg wash and sprinkle with a bit of sugar.
Eggwash (a beaten egg with a splash of milk)
Bake at 425° for 10 minutes. Reduce the temperature to 350° and continue baking for another 45 - 50 minutes.
Cool before cutting into the pie. Keep refrigerated, loosely covered.