If you’ve ever walked through small towns in Italy — or even noticed similar scenes in neighborhoods across Europe and beyond — you may have spotted something curious: plastic water bottles lined up outside doorways, garages, storefronts, or tucked into building corners. At first glance, it might look like litter, recycling set aside, or even a quirky local custom. But in many cases, these bottles are placed there intentionally, serving a very specific purpose: to stop dogs and cats from urinating on walls.

The Idea Behind the Bottles

In parts of Italy, this practice has circulated for years. Homeowners who use the method believe that clear bottles filled with water can deter animals from marking their property. The theory varies slightly depending on who you ask.

One explanation suggests that sunlight reflecting off the water creates shimmering light patterns that confuse or startle animals. Another claims that the reflection mimics the presence of another animal, making dogs or cats think the territory is already claimed. Some people also believe the bottles act as a subtle visual signal to pet owners — a kind of message that says, “Please don’t let your dog stop here.”

In short, the bottles are meant to discourage animals from choosing specific spots to urinate by creating a psychological or visual barrier.

Myth vs. Reality

Despite how widespread the habit has become, there is no solid scientific evidence proving that water bottles reliably deter dogs or cats. Animal behavior specialists generally agree that pets are not consistently influenced by light reflections in this way. Dogs, in particular, rely far more on scent than visual cues when marking territory.

While a bottle might occasionally coincide with reduced marking in a specific location, this is likely due to chance or other environmental factors — not the bottle itself. In many cases, animals simply ignore them.

This makes the bottle method more of a folklore solution than a proven behavioral strategy. It’s inexpensive, harmless, and easy to try, but its effectiveness remains questionable.

Why the Bottle Trick Persists

If it doesn’t truly work, why do so many people continue doing it?

Several reasons help explain its staying power:

• Simplicity: Fill a bottle with water and place it outside — no tools, chemicals, or training required.

• Low cost: It uses something most households already have.

• Placebo effect: When marking decreases (even temporarily), homeowners credit the bottles.

• Community influence: When neighbors adopt the practice, others assume it must be effective.

• Harmless experimentation: Since it poses no risk, many people think, “It can’t hurt to try.”

Traditions like this often spread informally, passed along through word of mouth rather than scientific backing.

More Effective Alternatives

If your goal is genuinely to prevent animals from marking your walls, there are more reliable approaches supported by animal behavior principles:

• Clean thoroughly and immediately: Use water and a mild, pet-safe enzymatic cleaner to remove scent traces. Animals are more likely to return if they can still smell previous markings.

• Apply pet-safe repellents: Commercial sprays or gels designed to deter pets can be effective when applied consistently.

• Install physical barriers: Low fencing, decorative grilles, stones, thorny plants, or shrubs make walls less accessible and less inviting.

• Use motion-activated deterrents: Devices that emit short bursts of water, sound, or light can discourage animals in real time.

• Promote responsible pet supervision: Encouraging pet owners to guide dogs toward appropriate areas makes a meaningful difference in shared spaces.

Although these methods may require more effort than placing a bottle outside, they tend to deliver more consistent and measurable results.

The Bottom Line

Plastic water bottles outside homes are a quirky and creative attempt to prevent animal marking — but there is no scientific proof that they actually work. The practice continues largely because it is simple, inexpensive, and visually convincing.

If you’re serious about keeping pets from urinating on your walls, proactive strategies such as cleaning, repellents, physical barriers, or motion-based deterrents are far more effective. While the bottle trick may offer peace of mind, practical solutions rooted in animal behavior are much more likely to protect your property in the long run.