Riddle: What has holes on each side, but can still can hold water ?

Question

A square has a side length of 7. On each corner, a quarter circle with radius 3 is constructed with the corner as its center. And on the midpoint of each side, a semicircle with radius 2 is constructed with the midpoint as its center. What is the difference between the orange shaded areas and the blue shaded areas?

Answer 1

Pipe

As water pipe has holes both sides but still can hold water.