Why are so many toilets splashing in China

Why do you have to pee when you hear water splashing?

... Darwin too

But: which came first - hen or egg? Perhaps the crux of the matter lies in an evolutionary basis in the broadest sense: In order to survive, our ancestors had to guard against all kinds of enemies. For this it was important to leave no traces as possible. Because of its pungent smell, urine was a kind of residue that had to be avoided at all costs if one did not want to lure said enemies onto one's own trail. So our shrewd ancestors relieved themselves as much as possible in rivers, creeks or just when it was raining. So the subconscious association of urination and rushing water could be an evolutionary relic that ensured the survival of our ancestors.

First relaxed, then relieved

Another explanation is neurological: water noises have a relaxing effect, stimulate the parasympathetic nervous system and therefore cause an urge to urinate. But first things first: We cannot consciously control the muscles of our bladder, at least not most of them. Instead, the bladder muscles are controlled by the autonomic nervous system. The parasympathetic nervous system tenses the muscles: the bladder contracts, we feel the urge to urinate. The sympathetic has the opposite effect. Because of him, the muscles relax so that the bladder relaxes and urine can collect.

When we are under stress, the sympathetic system has the upper hand. Logical, because if we have to flee or fight, we have no time for other urgent needs. If we are relaxed, the parasympathetic reigns and we can literally let things run free. And regardless of whether the sound of the sea or lawn sprinklers: Water noises of any kind should have a relaxing effect and could thus strengthen the parasympathetic nervous system, which in turn causes the urge to urinate.