Water. A city is always being washed by water, in its various forms: rain, sleet, hail, snow, streams, rivers, through fountains, baths, taps, sprinklers, gutters, gargoyles, spouts, hoppers, pipes, chains, channels, and drains.
The human body has the same density and salinity as sea water. If you breathe in you remain at the surface, if you breathe out you can sink a few feet - not far, without weights - a couple of kicks and you're back up again in the froth and spume of the breaking wave. We come as a species from the sea. We need salt, which has always been a basic tradeable commodity and necessity. We have a lot in common with dolphins, and seals. We do not belong to the sea,  we have climbed up onto land and stood upright . Yet our sense of the horizontal and vertical has developed to a high degree of sensitivity before birth, in a fluid filled environment; and the labyrinth of the ear - another fluid filled environment - gives each dimension (height, width, depth) an equality - each loop is the same size. Once in air and upright the vertical dimension plays quite differently from width and depth. Perhaps our dreams of flying are dreams of water.
The sound of water is at once fascinating and chaotic: predictable en masse but unpredictable in detail:  It speaks to us of its dirsturbance, movement, moment to the point of utterance. Water drips, drops, murmurs, mutters, pitter-patters, spits, trickles, babbles, burbles, fizzes, foams, froths, glugs, gurgles, pops, sloshes, spatters, splashes, sploshes, spurts, whines, ripples, cascades, crashes, crumps, crunches, pelts, roars, rushes, slushes, swishes, thunders: not only by itself but because of its enclosure and our enclosure as listeners.
Enclosed by our way of understanding things our culture, our mythology: because we have chosen to belong not to a group of buildings but to a living city 
Cities are voracious drinkers.
Take London, with 7 million inhabitants - its body corporate consumes about 200million gallons of water a day 30 gallons of water per citizen.