Fans turned out in droves to be a part of day one of the Melbourne-based grand slam on Monday, but not everybody was satisfied.
"In what universe do we need to import bottled water?"
Her comment, which featured pictures of the water labelled "Australian Open official water", was retweeted more than 500 times and received more than 250 comments.
"In a universe where the deal was worth millions of dollars a year to Tennis Australia," he wrote.
In a statement, Tennis Australia said the Australian Open was a global event with "a long history of partnering with international brands".
"Ganten water is a premium brand that is associated with other major tennis and sporting events," the statement said.
"No prize for guessing as to why that would be."
Others suggested the Open should ditch single-use plastic bottles altogether.
"Idea for next year: Ditch the one-use plastic, provide water fountains and if people don’t bring their own drink bottle make them buy one," Alexandra McKiernan wrote.
"No need to buy bottled water.