My cousing in Brazil tested it with flyes. And awsome, it works pretty well! We are in a place with many flyes and when he put a tranparent bag with water pending of ceiling, in less than two minutes the flyes gone away.
I can´t explain why, but just work. With dogs i think it will not work.

Thinking about, i suppose the reazon to a bag of water work with flyes. The flyes have an excellent olfative system. May be the water smell can occlude and confund the food (trash, or anything else) smell in air. Without the smell or pheromon enough in air, the flyes tend to ampliate the area of seek food, and they gone away of the water bag perimeter.

I dont know if is right, but appear to be a good theoric explanation.

Please, put the Brasilia Cathedral (Brazil)
http://www.caminandosinrumbo.com/brasil/brasilia/imagenes/Brasilia1.jpg
And

Rio de Janeiro Cathedral
http://www.rioon.com/fotos/catedral1.jpg

It´s awsome