Roland comes upon a saner-than-most border dweller named Brown who lives alone except for his pet raven, Zoltan.
The gunslinger is thirsty, lonely, and his mule is nearly dead. Brown (who I always find myself suspicious of because of his red hair--when that color comes up in King's books, I steel myself ... even if I've read it a ridiculous number of times) explains that he's happy to share his corn, but Roland will have to contribute something for the beans, which are rarer as Brown has to get them from someone else. When Brown goes off to prepare dinner, he suggests that Roland fill his waterskins from his well.
As Roland is in the process of replenishing his water supply, he is shocked when Zoltan squawks, "Screw you and the horse you rode in on." At the sound of the raven's voice, Roland is suddenly aware of how easy it would be for Brown to throw a rock down the well, killing or seriously injuring the gunslinger.
Death in a well is a revisit of sorts. King used this image effectively in his novel Dolores Claiborne, where a woman backed into a corner by her manipulative child-molester of a husband gives him the only justice she can--a rock to the head.
Although this is momentarily reminiscent of a very different novel, Brown does not attack Roland as he's filling his waterskins, and the gunslinger pushes the idea out of his mind with the old adage, "There will be water if God wills it."