"When you grind coffee and mix it with water, lots of different things in the water – calcium, magnesium, bicarbonate – have a huge influence on how the coffee is extracted," which in turn affects how it tastes, the shop's Colin Harmon said to the Independent.

For example, Harmon says people buy bags from the shop that don't taste the same when brewed at home, likely because of the water.

The tasting started because the shop wanted "to get people thinking about water" he told the website.

But what started as a fun experiment ended up backfiring on 3FE, he writes on the coffee shop's blog.

There were complaints about the price, to which Harmon says the tasting water couldn't be given away for free. (The shop offers filtered water free of charge.)

Of the 30 tastings so far, the feedback has been generally positive. It also makes for a great conversation piece, he says.

The backlash came when he read Internet comments that featured a "relentless onslaught of condemnation."

So his solution is to donate all proceeds from the water tasting to Wells for Zoe, an Irish charity which aims to bring people in Africa access to clean water. On top of that, the shop will also match the donation.