Airports can be expensive for food and drink, but what happens when customers are trusted with an 'honesty station'?

That's what Dublin Airport introduced in 2014, when its first 'Plane Water' stations popped up in a number of post-security locations.

The water is freely available on unmanned service kiosks, with a listed price of €1 and a coin box clearly located beside the display.

And the results?

92pc of passengers pay the €1, the airport says.

"Passengers love the value and convenience of the system, and daa quickly implemented the concept at Cork Airport as well," it adds.

One euro at Dublin airport Plane water 500ml. Other airports should take note.... Zurich, Faro, Basel pic.twitter.com/UkILuuGBr9 — Nick Greeves (@nickgreeves) April 6, 2016

The idea has since been taken up in other airports including Brussels, according to daa, and passers-by have had some interesting reactions.

"The reciprocity effect suggests that if people perceive the Plane Water as a kindness on the part of the airport authority, they may respond by displaying more kindness themselves," wrote Amy Bucher on this blog post after her visit.

Just saw 2 people take the Plane Water in Dublin airport and not put any money in.Who does that??What is happening to the world? #planewater — Marion Ryan (@MarionRyan410) September 5, 2016

"If you’re an enterprising Irish psychology student looking for a quick class project, please consider studying this!"

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