Starbucks Wasting More Than 6 Million Gallons of Water a Day

Apart from the wastage itself, there are potentially other environmental effects. Tompkins said the energy used to pump water from the ground and treat it increases the carbon footprint of the entire operation.

While the company states it is in compliance with the World Health Organization, the U.S. Environmental Protection Agency and European Union standards, Starbucks admitted that "the opportunity exists to reduce our total water usage."

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Tompkins said, "It's really good that they have customer health in mind," but he added that there are other ways to ensure cleanliness and hygiene in its stores.

Tompkins said the aim of his organization is to "reduce waste, not restrict use" and noted that Starbucks deserved credit for its "really good customer health record."

But he also offered some advice on how Starbucks could reduce its water waste and still ensure its stated commitment to customer safety.

He said the company could cut water use when the stores are not extremely busy and also look into ways of "lowering the flow" of water, such as aerating nozzles.

"They can do a water audit and discuss [it] with their staff," he said.

In the statement to ABC News, Starbucks said it has tested more environmentally-friendly ways to maintain its hygiene, including using an ice bath and eliminating spoons altogether.

"Neither of these alternatives was successful," the statement said.

Starbucks stated that other methods are "currently under consideration," including using dishwashers to clean their utensils.

"We continue to routinely re-evaluate our equipment, store design and training opportunities to reduce our overall water use with the goal of ultimately reducing our environmental footprint," the company said.