Don't forget to clamp (or band/zip-tie) whatever you're sculpting before it starts to cure - IME WaterWeld mushrooms more than most two-part molded epoxies and you'll get weak joins that pop loose in the months to come if you don't.
If possible, work with & allow it to cure dry for added strength & to spare your skimmer. And maybe pack some sand/rubble into the surface of the joins if they're clearly visible - seams really never seem to get covered in coraline even though my tank's lousy with the stuff.
But yes, it's rated drinking water safe and I've been using it for years in both my nano & pico tanks.