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To borrow some phrasing from a popular beer ad: I don’t always drink club soda, but when I do, I never know what I’m going to be charged. Some bartenders treat the non-alcoholic beverage like a sober driver’s special and will pass it along for the price of a water: free. Other places seem to think, hey, it came out of the soda fountain, so they charge you soda rates. Based on my experience, prices can depend not only on where you go, but who you order from and sometimes even what time of day.

A British group called Club Soda that advocates for responsible drinking recently confirmed that my experience is more than just anecdotal; it’s typical. It conducted a study around London pubs, ordering a soda water and lime cordial at different establishments across the city. According to co-founder Laura Willoughby, prices for the drink varied greatly, anywhere from about 40 cents to as much as about $6.50 – as much as a beer. “The worst example was a bar so unused to serving soft drinks it randomly priced every lime and soda we had,” she told the Standard. “There we paid from nothing to £2.50 a half pint.”

Asked by The Sun, JD Wetherspoon, an ownership group with nearly 1,000 pubs, said that at any of their locations a pint of lime cordial and soda should cost a little over a buck. “Prices are set by Wetherspoon,” a spokesman said. “They may vary from region to region but not by much.” But as Club Soda’s study shows, setting prices means nothing if the bartenders don’t know them or follow them (this particular study doesn’t have information as to whether this is happening at Wetherspoon’s bars).

And in the US, we have another major factor that likely drives fluctuation: tipping. I haven’t run any studies, but tossing down a couple extra bucks for your first soda is often a good way to keep the soda gun firing fast and loose.

In the end, Club Soda’s study speaks to another larger point though: Yes, bars are business, but they are also in the business of trying to keep their patrons drinking responsibly. If an establishment is charging as much for a non-alcoholic drink as a pint of beer, it might leave a nasty lime cordial taste in some of the more responsible drinkers’ mouths.