Wash the fruit and set aside. Add the water and lemon juice to a large bowl.

For each apple, remove the core with an apple corer or small paring knife. Turn the apple on its side, and slice into 1/4" rings. As soon as they're sliced, place in the bowl of acidified water. This helps keep them from turning brown.

For each pear, you can repeat the coring process -- though I sliced them in half (from top to bottom), and then cut out the core, and cut them into half-rounds instead. Add them to the water, too.

Optionally, dust them with ground cinnamon or other spices (nutmeg? clove?).

If you're lucky enough to have your parents' dehydrator, lay the fruit in a single layer on the trays in the dehydrator. Cover, turn it on, and walk away. Come back in four hours and check on things -- it'll probably take a total of 6 to 10 hours. You may need to remove some sooner than others.

You can also dry these in the oven. Line a baking sheet with parchment paper, and lay the slices flat on top. Bake at the lowest setting your oven will go (about 175-200), for approximately 2 to 6 hours (depending on the temperature and how thick you've sliced them). Just keep an eye on them every couple of hours; you may need to remove some sooner than others.