"I can't pee", you say as a mother or father watches over and insists that you have do. After sitting on the toilet and arguing with your parents about wanting to just go to bed, they turn the faucet on in the bathroom and within seconds the urge to pee enters your mind as you hear the water shooting out and splashing into the sink.
Why is it that the sound of running water enhances our need to urinate? Although the main reason is unclear, it seems to be a psychological phenomena that we develop, perhaps, ironically, because of moments where our parents tell us that running water will make us pee.
Or it could be an association that we build up on our own. The sound of running water can be similar to the sounds we hear while urinating, and thus we have inadvertently built up a psychological connection between the two actions.