Preheat oven to 350 degrees F (175 degrees C).

Toss apples with lemon juice and water in a shallow 2 quart baking dish.

In a large bowl, combine flour, oats, sugar, nutmeg, and salt. Mix to blend thoroughly. Cut in the butter or margarine until mixture resembles coarse crumbs. Mix in walnuts. Crumble over apples to cover completely.

Bake for 40 to 45 minutes until top is lightly browned. Serve warm or at room temperature.