The crash of ocean waves, the babbling of brooks, the pitter-patter of rain on shingles — many people swear by these watery sounds to help them fall asleep and stay in la-la land. Why does flowing “agua” apparently have such a powerful and popular drowsing effect?
Part of the answer lies in how our brains interpret the noises we hear — both while awake and in the dead of night — as either threats or non-threats.
Dispatches From The Front 