Wash, peel, and core the apples. Slice them into thin wedges, about 1/4 inch thick. This helps them cook evenly and fit well in the jars.

In a large bowl, toss the sliced apples with lemon juice to prevent browning.

In a large pot over medium heat, combine the sliced apples, granulated sugar, brown sugar, flour, cinnamon, nutmeg, salt, and water. Stir well to coat the apples.

Cook the mixture for about 5-10 minutes, stirring occasionally, until the apples are just tender but not mushy. This step helps to release the juices and thicken the filling.

While the apple filling is cooking, sterilize your canning jars by placing them in boiling water for 10 minutes. Keep them hot until ready to fill.

Prepare the lids according to the manufacturer's instructions, usually by simmering them in hot water.

Using a ladle and canning funnel, fill each sterilized jar with the hot apple filling, leaving about 1 inch of headspace at the top. This space is necessary for the expansion of the filling during processing.

Wipe the rims of the jars with a clean cloth to remove any residue that could prevent sealing.

Place a lid on each jar and screw on the band until it's fingertip tight. Do not overtighten, as this can prevent proper sealing.

Place the filled jars in a boiling water canner. Ensure the jars are covered by at least 1 inch of water.

Bring the water to a boil and process the jars for 20 minutes for quarts. Adjust the time for altitude if necessary (add 5 minutes for every 1,000 feet above sea level).

After processing, carefully remove the jars using a jar lifter and place them on a clean towel or cooling rack. Allow them to cool completely for 12-24 hours.

Once cooled, check the seals by pressing down in the center of each lid. If it doesn't pop back, the jar is sealed. If it pops back, refrigerate and use within a week.

Store sealed jars in a cool, dark place. Properly canned apple pie filling can last up to a year.