The signs say to please wear shoes, and to walk. On a recent afternoon, hardly anyone listens. Hot, humid days like this? The pull of the water is irresistible; the swarming kids can’t douse themselves fast enough. We’re at the Children’s Fountain on the Christian Science Plaza downtown, an urban summer refuge since 1975. By my count, 180 separate sprinklers, arranged around the perimeter of a circle, shoot arcs of cool water toward the center (some 22,000 gallons a day). What you hear most are the squeals of delight and relief. Summer camps come here, as do families, with parents often watching from the sidelines. Some adults do away with the just-for-kids pretense and soak themselves, too. All around, the city heaves and whirs. MBTA buses rev and squeak, Huntington Avenue hums with life, and church bells mark the hour. Inside this wet sanctuary, all of that, for the moment, falls away. What’s left are the sounds of pure glee — the white-noise hiss of the sprinklers, the reverberating laughter, and the smack-smack of bare feet scampering across the brick.