In a bold move toward pollution control, San Francisco has just become the first city in America to ban the sale of plastic water bottles, a move that is building on a global movement to reduce the huge amount of waste from the billion-dollar plastic bottle industry. Over the next four years, the ban will phase out the sales of plastic water bottles that hold 21 ounces or less in public places. Waivers are permissible if an adequate alternative water source is not available. Joshua Arce, chairman of the Commission on the Environment, said the ban is “another step forward on our zero-waste goal.” The City wants to have no waste going to its landfill by 2020. Its diversion rate now stands at 80 percent. Past efforts toward the goal included banning plastic bags and plastic-foam containers. “We had big public events for decades without plastic bottles and we’ll do fine without them again,” Arce said.