Cheesy Chicken, Broccoli and Rice Casserole

4 cups broccoli florets (from about 1 pound)

3 tablespoons water

4 tablespoons butter

4 tablespoons flour

3 cups 1% milk

2 cups (8 oz) shredded cheddar cheese

salt and freshly ground pepper,

4 cups cubed cooked chicken (from about 2 pounds, ~3-4 chicken breasts)

3 cups cooked rice

for the topping

1 cup (4 oz) shredded cheddar cheese

2 cups cereal - Post Honey Bunches of Oats Almond

4 tablespoons butter, melted