As someone with the metabolism of a racehorse on methamphetamine, I'm blessed with the need to pee all the damn time. Luckily, I've never been too late, but I do generally plan my outdoor activities around the nearest public restroom.
One time, I was at Yosemite National Park, admiring a beautiful waterfall, when the rhythmic downpour of rushing water made me dash off in search of the nearest outhouse. The urge to pee in the presence of running water isn't weird. Most people are probably familiar with this sensation, so there must be some scientific basis for the phenomenon.
Thankfully, the folks over at SciShow have trickled a little bit of light on the connection in their latest video.
The hypothetical answer, according to psychologists and urologists, has everything to do with a principle you learned about in high-school biology: classical conditioning, or the experiment demonstrated by Russian psychologist Ivan Pavlov and his dogs.
Classical conditioning is a learning theory that relies on automatic response mechanisms to explain why animals (including us) react to certain things seemingly subconsciously.
So, as the most famous example goes, Pavlov's dogs naturally salivated around food. Knowing this, the psychologist rang a bell every time he gave his dogs their daily meals. Over time, the dogs learned to associate the sound of a bell ringing with meal-time. And, eventually, the clang of the bell without the presentation of food was enough to make them drool. All of this is controlled by a neural network called the autonomic nervous system.
Likewise, when it comes to running water and peeing, the theory is that we've simply been conditioned to play out a specific response to a particular stimulus. Peeing sounds like tinkling water, ergo a leaky faucet reminds us that we need to go. Some reflexes can be hard-wired, such as catching yourself when you fall, but others can be learned through repetition.
Surprisingly, there's relatively little scientific research on the role that classical conditioning plays in this peepee phenomenon. But parents trying to potty train their toddlers and patients suffering from "shy bladder syndrome" are often encouraged to let the sink run to get things going. According to SciShow, even a photograph of falling water can be enough to elicit a steady stream.
If the Pavlovian argument is true, you could theoretically also desensitize your mind the sound of water. Using cognitive behavioral therapy, a person could counter-condition themselves to replace an unwanted response (peeing) with an acceptable one. This training technique is often used to curb bad behavior in dogs, although it's never worked on my own hound.
So if you're really worried about a babbling brook setting you off, you might have some options. Otherwise, maybe just go before leaving your house?