Coarsely chop the apples (do not peel or core). Place blueberries in a 10-quart heavy pot; crush slightly with a potato masher. Add apples and the water. Bring to boiling. Boil gently, uncovered, 20 minutes, stirring occasionally.
Line a large colander or sieve with a double layer of 100-percent-cotton cheesecloth; place over a large bowl. Pour apple mixture into colander. Let stand about 30 minutes or until juices stop dripping (avoid squeezing juice from cheesecloth; this can cause cloudy jelly). Measure 4 cups juice. Discard fruit.
In the same pot combine the apple-blueberry juice and the sugar. Bring to a full rolling boil, stirring to dissolve sugar. Boil hard, uncovered, about 15 minutes or until jelly sheets off of a metal spoon and reaches 220 degrees F. Remove pot from heat. Quickly skim off foam with a metal spoon.
Ladle hot jelly into hot, sterilized half-pint canning jars, leaving a 1/4-inch headspace. Wipe jar rims; adjust lids and screw bands.
Process filled jars in a boiling-water canner 5 minutes (start timing when water returns to boiling). Remove jars from canner; cool on wire racks until set.