Preheat the oven to 425 degrees F (220 degrees C). Arrange one pie crust in a 9-inch pie plate.

Toss peaches and blueberries in a bowl with lemon juice. Mix sugar, tapioca, and salt in a small bowl and add to peach mixture; stir to combine. Allow fruit to rest for 15 minutes.

Transfer fruit into prepared pie crust. Scatter butter pieces over fruit and brush the edge of the pie with water. Cover pie with remaining crust; press and seal the top and bottom crusts.

Bake in the preheated oven until crust is golden brown and fruit is bubbly, 45 to 50 minutes.