Peel and de-core the apples. Thinly slice and set in a large bowl. Coat with the lemon juice and toss to combine.
In a small bowl, mix together the sugar, cornstarch, cinnamon, nutmeg and salt. Set aside.
In a large pot or dutch oven, pour the 4 ½ cups of water and bring to a boil. Add the dry cornstarch mixture and reduce the heat. Simmer for 1 minute or until the sauce starts to thicken.
Add the sliced apples to the pot and gently stir to evenly coat with the sauce. Cover and continue to simmer until the apples are tender, about 10 minutes. Remove from heat and allow to cool.
Once cooled, divide the pie filling into two freezer safe containers or pour a single portion directly into the prepared pie crust for baking. Pie filling may be stored in an airtight container in the refrigerator for up to 4 days or in the freezer for up to 12 months.