Three years ago, the University of Vermont in Burlington began to experiment with a few nudges towards a healthy, sustainable lifestyle. First, in 2012, campus outlets and the company operating the vending machines were required to make sure that at least 30 per cent of the drinks on offer were wholesome stuff such as vegetable juice, low-fat milk and water. A few months later, selling bottled water on campus was banned outright. The aim, pushed hard by student campaigners, was to encourage students to fill reusable bottles with tap water instead.

So, how did the Vermont experiment go? A study by Elizabeth Berman and Rachel Johnson (of the University’s own Department of Nutrition and Food Sciences) was recently published in the American Journal of Public Health. The researchers found that “per capita shipments of bottles, calories, sugars and added sugars increased significantly when bottled water was removed . . . As bottled water sales dropped to zero, sales of sugar-free beverages and sugar-sweetened beverages increased.”

In other words, the policy backfired with both barrels. Students didn’t switch to tap water, they switched to the likes of Coke and Diet Coke instead. All this would be just an amusing curiosity — one more example of student campaigners who are all heart and no brains — if it weren’t for the fact that more mature policy makers often commit similar blunders on much broader canvases. We would do well to learn some lessons from the University of Vermont’s experience.