[0] Photo is specifically from Iglesia de San Juan: http://www.atlasobscura.com/places/iglesia-de-san-juan-chamu... Apparently, Coca Cola is a choice to use alongside alcohol. I can't find mention of other places doing it.

[1] If the water is unsafe to drink, why would they not just boil it? That's how the vast majority of the world makes their water potable (especially tea).

I'm not saying Coca-Cola is free from wrongdoing, but the evidence of malice is very apocryphal. In my experiences in the third world, Coca-Cola was the only soft drink available, and people genuinely seemed to just really like soft drinks.

Heck, we have trouble getting Americans to drink water over soft drinks.