San Francisco International Airport is banning the sale of single-use plastic water bottles.

The unprecedented move at one of the major airports in the country will take effect August 20, the San Francisco Chronicle reported Friday.

The new rule will apply to airport restaurants, cafes and vending machines. Travelers who need plain water will have to buy refillable aluminum or glass bottles if they don't bring their own.

As a department of San Francisco's municipal government, the airport is following an ordinance approved in 2014 banning the sale of plastic water bottles on city-owned property.

The shift away from plastics is also part of a broader plan to slash net carbon emissions and energy use to zero and eliminate most landfill waste by 2021, said airport spokesman Doug Yakel.

But, considering the approximately 4 million plastic water bottles sold per year at the airport, it may be more difficult for vendors to adhere to the water bottle ban.

Whether vendors out of compliance will be penalized is unclear, but Yakel said the airport hopes that "won't be necessary."

SFO vendors already are required to provide only compostable single-use foodware, including to-go containers, condiment packets, straws and utensils.

Shops at the airports have adjusted easily to these requirements because of the increased availability of suppliers producing such products, said Michael Levine, CEO of the company that oversees Napa Farms Market, a store selling grab-and-go fare in Terminal 2 and International Terminal G.

"But the water bottle impact is a little trickier," he said.