Thanks for the tips
@Matttoadman and
@Hisserdude! I could imagine a beautiful enclosure with a waterfall or some other source of running water for these roaches, but this would be out of my budget right now.

But I keep your suggestions in mind, and perhaps in the future I can make a semi-aquatic display.
@Hisserdude is the problem with the standing water was your own experience or did you read it somewhere? I'm only asking because if it's in a book or paper I would love to read it, I'm always trying to learn new things about insects. And if it is your own experience, then thanks a lot for sharing this valuable information!