Do we know how difficult the rainfall problem is?

The programming task known as the Rainfall Problem has developed a reputation for being surprisingly difficult for introductory-level (CS1) students. We contribute a survey of studies of the problem as well as a new study of students' solutions collected at three institutions. In all three CS1s, at least about half of the students were able to fully solve the problem and the large majority were at least close. Failure to handle invalid or missing input accounted for most bugs. Our survey and study together suggest that the Rainfall Problem is not necessarily overwhelmingly difficult: Success rates vary and some reasonably good results have been achieved under multiple programming paradigms. We provide a breakdown of confounding factors and suggest improvements and hypotheses for future studies of the Rainfall Problem.