The difficulty of behavioral change

Via Robin Hanson, people can use sunlight to cheaply disinfect water, but in Bolivia they choose not to. Why?

The leader of the study, Daniel Mausezahl, suspects a big reason for this is that lining up water bottles on your roof shows your neighbors that you aren’t rich enough to have more expensive methods of disinfecting water.

This commenter posits some alternative explanations, but I don't find the "appearing poor" explanation implausible. Changing behavior is d*$! hard, as we know from other the difficulty of capturing other "low-hanging fruit" like energy efficiency. My latest favorite example is food waste - estimates vary widely, but the consensus appears to be in the neighborhood of 40% of all food is wasted globally. That means that to increase world food production by 10% (something we will definitely have to do in the next decade, with increasing affluence changing diets and demand for biofuels growing, on top of population growth), we could either farm another ~150m hectares (an area slightly smaller than Alaska, or Mongolia), or we could reduce food waste by 15%. The numbers look to so easy on paper, and yet the opportunity is so diffused that it is nearly impossible to act on it in an impactful way.

(Same goes, by the way, for those who propose the entire earth become vegetarian - how, exactly, are you going to convince people to do that?)

Update: Speaking of the difficulty of capturing energy efficiency gains, here's a good case example - the U.S. Department of Energy.

Update 2: It really is too easy to find examples of this - here is U.S. Food Policy on the challenge of encouraging kids to drink water instead of sugary drinks. Aliza rightly calls out the challenge of aligning this campaign with the campaign to move from bottled to tap water, because bottled water is bad.