Why is it that when you hang clear plastic bags of water, it keeps the flies away?

My friend told me it would work, and we tried it, and it did. I didn't believe it would work. But, why DOES it work? Are flies afraid of water? Please dish! Why is it that when you hang clear plastic bags of water, it keeps the flies away?
they can sense motion and avoid moving objects. Filled bag is a huge glittering object (for fly) This is a survival strategy. When you try to hit a fly it escapes. The fly should escape moving targets (chameleon's tongue for example) immediately. Plastic bags do exactly the same, distracts the flies (like a scarecrow for crows) Why is it that when you hang clear plastic bags of water, it keeps the flies away?
the rebelution