Well, isn’t that an interesting question? You may be thinking that you are not going to eat the rind so why do you need to waste the time washing the exterior of a melon?
But, think about it for just a second. Melons and squashes grow on a vine on the ground. That means dirt, manure, fertilizer, etc. Then they are picked and moved around by hand from the field to the time you get it home. It’d be nice to think that everyone and everything it came into contact with was clean, but they are not.
Then you take that melon or squash, place it on your cutting board and cut through it. If the exterior has not been washed then whatever is on the outside travels straight through to the center. Yuck!
So, note to self, wash your melons!