to keep flies away

Does a plastic bag filled with water and hung out somewhere really repel flies? If so, why/how?

Apparently, it’s not uncommon in Mexico and the US Southwest to hang a plastic baggie filled with water in restaurants and such places to keep flies away. There are a couple of people on the Internet in business selling products that are basically plastic bags filled with water, only they’re somehow special plastic bags, so you should pay those people, according to their web pages. Will any plastic bag work?

This was discussed a couple of days ago, so I’ll close this thread and direct further comment to an earlier thread: Water in a bag keeps flies away??

bibliophage
moderator GQ