I'm no roach expert (except for back in my college days ^_^ ) but my understanding is that roaches are VERY attracted to water. They can get by without food for quite some time but water is a necessity. They die w/out it like everything else...

I've considered covering the freshwater but was concerned about the water getting moldy (though I am running a small powerhead in there).

I was wondering if I should (carefully) spray the outsides of my container with some kind of repellant. Perhaps I won't worry about it until/unless I see a roach.