Here’s Why You Should Hang Bags Full of Water on Your Porch
If you’ve ever seen clear plastic bags filled with water hanging from a porch, doorway, or outdoor seating area, you may have wondered what they were supposed to do. It might look unusual, but there’s a simple reason people use this old-fashioned trick: they believe it can help discourage flies and other small flying insects.
How Is a Bag of Water Supposed to Work?
The idea is that light passing through the water-filled bag creates reflections and changing patterns that may confuse or disturb flies. Some versions of the trick also suggest that the enlarged reflections produced by the water resemble the appearance of predators or other threats to insects.
You’ll often see the method used around outdoor dining areas, patios, porches, and entrances—especially during warm weather when flies are more active.
However, it’s important to understand that the evidence for this method is limited. There is no strong scientific proof that hanging water bags reliably keeps flies away. Flies are attracted to food, garbage, animal waste, and other odors, so a water bag should not be considered a replacement for proper sanitation or insect control.
How People Try the Trick
If you want to experiment with it, the setup is straightforward:
- Fill a transparent plastic bag about halfway to three-quarters full with clean water.
- Seal the bag tightly so it doesn’t leak.
- Hang it near a porch, doorway, window, or outdoor eating area.
- Keep it somewhere where it won’t be easily knocked down or exposed to sharp objects.
- Replace the bag if it becomes cloudy, dirty, or damaged.
Some people place a few shiny objects, such as coins, inside the bag because they believe the reflections make the method more effective. There isn’t good evidence that adding coins makes a meaningful difference, though.
Why It Might Seem to Work
There are several possible explanations for why people report success. Reflected sunlight can create moving flashes and distortions, and insects perceive light differently from humans. These unusual visual patterns may potentially affect their behavior.
But results can vary considerably depending on the environment. A porch with food scraps, overflowing garbage, standing water, or other strong attractants may still have plenty of flies regardless of whether water bags are hanging nearby.
Better Ways to Reduce Flies
For a more dependable approach, combine simple prevention methods:
- Keep garbage bins tightly covered.
- Clean food spills promptly.
- Don’t leave pet food outside for long periods.
- Keep doors and windows screened when possible.
- Remove standing water.
- Clean outdoor eating areas regularly.
- Keep compost and food waste properly contained.
The Bottom Line
Hanging bags of water on a porch is an inexpensive household trick that some people swear by, particularly for reducing flies around outdoor areas. But it should be viewed as a traditional DIY experiment rather than a scientifically proven insect-repellent method.
If you try it, there’s little reason to expect dramatic results—but when combined with good cleanliness and proper insect prevention, it may be worth testing to see whether it makes a difference around your own porch.