I would think it takes very little mental RAM space to figure out that sidewalks in Manhattan get copious daily deposits of urine, feces, vomit, spit, garbage, soot, grime, and God knows what other unpleasant stuff from millions of people (residents, commuters, tourists), dogs, birds, rats and other members of the local fauna. So when it rains hard enough to create bubbling streams of water running along the curb toward the nearest storm drain, even borderline retards among us should know that this is not the kind of water you want to make contact with your skin, let alone your face and/or genitalia.
Any adult who does not know this is a living proof that something may be wrong with the concept of evolution by natural selection. The genotype of the two happy twenty-somethings in the photo below - taken in Times Square shortly after the hurricane Irene passed through Manhattan - should have been "de-selected" long time ago because it produces such staggering stupidity at the phenotype level.