Preheat oven to 350 degrees F.
Combine pears, water and lemon juice in an 8 by 8-inch baking pan. In a bowl, combine oats, flour, sugar and cinnamon. Pour in the melted butter and stir to make a crumbly mixture. Spread the topping evenly over the fruit. Bake for 45 to 55 minutes or until the topping is crisp and browned.