At Rainbow Grocery, a cooperative in this city’s Mission District, one brand of water is so popular that it’s often out of stock. But one recent evening, there was a glittering rack of it: glass orbs containing 2.5 gallons of what is billed as “raw water” — unfiltered, untreated, unsterilized spring water, $36.99 each and $14.99 per refill, bottled and marketed by a small company called Live Water. “It has a vaguely mild sweetness, a nice smooth mouth feel, nothing that overwhelms the flavor profile,” said Kevin Freeman, a shift manager at the store.